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In the field of computing, the term spyware refers to a broad category of malicious software designed to intercept or take partial control of a computer's operation without the informed consent of that machine's owner or legitimate user. While the term taken literally suggests software that surreptitiously monitors the user, it has come to refer more broadly to software that subverts the computer's operation for the benefit of a third party.

In simpler terms, spyware is a type of program that watches what users do with their computer and then sends that information over the internet. Spyware can collect many different types of information about a user. More benign programs can attempt to track what types of websites a user visits and send this information to an advertisement agency. More malicious versions can try to record what a user types to try to intercept passwords or credit card numbers. Yet other versions simply launch popup advertisements.


History and development

The first recorded use of the term spyware occurred on October 17, 1994 in a Usenet post that poked fun at Microsoft's business model. Spyware later came to refer to espionage equipment such as tiny cameras. However, in early 2000 the founder of Zone Labs, Gregor Freund, used the term in a press release for the ZoneAlarm Personal Firewall. [1] Since then, computer-users have used the term in its current sense.

In early 2000, Steve Gibson of Gibson Research realized that advertising software had been installed on his system, and he suspected that the software was stealing his personal information. After analyzing the software he determined that they were adware components from the companies Aureate (later Radiate) and Conducent. He eventually retracted his claim that the ad software collected information without the user's knowledge, but still chastised the ad companies for covertly installing the spyware and making it difficult to remove.

As a result of his analysis in 2000, Gibson released the first anti-spyware program, OptOut, and many more software-based antidotes have appeared since then. [1] International Charter now offers software developers a Spyware-Free Certification program. [2]

According to a November 2004 study by AOL and the National Cyber-Security Alliance, 80% of surveyed users' computers had some form of spyware, with an average of 93 spyware components per computer. 89% of surveyed users with spyware reported that they did not know of its presence, and 95% reported that they had not given permission for the installation of the spyware. [3]

As of 2006, spyware has become one of the preeminent security threats to computer-systems running Microsoft Windows operating-systems (and especially to users of Internet Explorer because of that browser's collaboration with the Windows operating system). Some malware on the Linux and Mac OS X platforms has behaviour similar to Windows spyware, but to date has not become anywhere near as widespread. In an estimate based on customer sent scan logs, Webroot Software, makers of Spy Sweeper, said that 9 out of 10 computers connected to the internet are infected and 86% of those surveyed suffered a monetary loss due to spyware.[4]

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Spyware, adware, and tracking

The term adware frequently refers to any software which displays advertisements, whether or not it does so with the user's consent. Programs such as the Eudora mail client display advertisements as an alternative to shareware registration fees. These classify as "adware" in the sense of advertising-supported software, but not as spyware. Adware in this form does not operate surreptitiously or mislead the user, and provides the user with a specific service.

Many of the programs frequently classified as spyware function as adware in a different sense: their chief observed behaviour consists of displaying advertising. Claria Corporation's Gator Software and Exact Advertising's BargainBuddy provide examples of this sort of program. Visited Web sites frequently install Gator on client machines in a surreptitious manner, and it directs revenue to the installing site and to Claria by displaying advertisements to the user. The user experiences a large number of pop-up advertisements.

Other spyware behaviours, such as reporting on websites the user visits, frequently accompany the displaying of advertisements. Monitoring web activity aims at building up a marketing profile on users in order to sell "targeted" advertisement impressions. The prevalence of spyware has cast suspicion upon other programs that track Web browsing, even for statistical or research purposes. Some observers describe the Alexa Toolbar, an Internet Explorer plug-in published by Amazon.com, as spyware (and some anti-spyware programs report it as such) although many users choose to install it.

Spyware, virus and worm

Spyware differs from viruses and worms in that it does not usually self-replicate. Like many recent viruses, however, spyware — by design — exploits infected computers for commercial gain. Typical tactics furthering this goal include delivery of unsolicited pop-up advertisements; theft of personal information (including financial information such as credit card numbers); monitoring of Web-browsing activity for marketing purposes; or routing of HTTP requests to advertising sites.

Routes of infection

Spyware does not directly spread in the manner of a computer virus or worm: generally, an infected system does not attempt to transmit the infection to other computers. Instead, spyware gets on a system through deception of the user or through exploitation of software vulnerabilities.

The most direct route by which spyware can infect a computer involves the user installing it. However, users tend not to install software if they know that it will disrupt their working environment and compromise their privacy. So many spyware programs deceive the users, either by piggybacking on a piece of desirable software such as Kazaa, or by tricking the users to do something that installs the software without them realising. Recently, spyware has come to include "rogue anti-spyware" programs, which masquerade as security software while actually doing damage.

Classically, a Trojan horse, by definition, smuggles in something dangerous in the guise of something desirable. Some spyware programs get spread in just this manner. The distributor of spyware presents the program as a useful utility — for instance as a "Web accelerator" or as a helpful software agent. Users download and install the software without immediately suspecting that it could cause harm. For example, Bonzi Buddy, a spyware program targeted at children, claims that:

He will explore the Internet with you as your very own friend and sidekick! He can talk, walk, joke, browse, search, e-mail, and download like no other friend you've ever had! He even has the ability to compare prices on the products you love and help you save money! Best of all, he's FREE! [5]

Spyware can also come bundled with shareware or other downloadable software, as well as music CDs. The user downloads a program (for instance, a music program or a file-trading utility) and installs it, and the installer additionally installs the spyware. Although the desirable software itself may do no harm, the bundled spyware does. In some cases, spyware authors have paid shareware authors to bundle spyware with their software. In other cases, spyware authors have repackaged desirable free software with installers that add spyware.

A third way of distributing spyware involves tricking users by manipulating security features designed to prevent unwanted installations. The Internet Explorer Web browser, by design, prevents websites from initiating an unwanted download. Instead, a user action (such as clicking on a link) must normally trigger a download. However, links can prove deceptive: for instance, a pop-up ad may appear like a standard Windows dialog box. The box contains a message such as "Would you like to optimise your Internet access?" with links which look like buttons reading Yes and No. No matter which "button" the user presses, a download starts, placing the spyware on the user's system. Later versions of Internet Explorer offer fewer avenues for this attack.

Some spyware authors infect a system by attacking security holes in the Web browser or in other software. When the user navigates to a Web page controlled by the spyware author, the page contains code which attacks the browser and forces the download and installation of spyware. The spyware author would also have some extensive knowledge of commercially-available anti-virus and firewall software. This has become known as a "drive-by download", which leaves the user a hapless bystander to the attack. Common browser exploits target security vulnerabilities in Internet Explorer and in the Microsoft Java runtime.

The installation of spyware frequently involves Microsoft's Internet Explorer. As the most popular Web browser, and with an unfortunate history of security issues, it has become the largest target. Its deep integration with the Windows environment and its scriptability make it an obvious point of attack into Microsoft Windows operating systems. Internet Explorer also serves as a point of attachment for spyware in the form of browser helper objects, which modify the browser's behaviour to add toolbars or to redirect traffic.

In a few cases, a worm or virus has delivered a payload of spyware. For instance, some attackers used the W32.Spybot.Worm worm to install spyware that popped up pornographic ads on the infected system's screen. [6] By directing traffic to ads set up to channel funds to the spyware authors, they can profit even by such clearly illegal behaviour.

Effects and behaviours

A piece of spyware rarely "lives" alone: an affected computer can rapidly become infected with large numbers of spyware components. Users frequently notice unwanted behavior and degradation of system performance. A spyware infestation can create significant unwanted CPU activity, disk usage, and network traffic which thereby slows down legitimate uses of these resources. Stability issues, such as application or system-wide crashes, are also common. Spyware which interferes with networking software commonly causes difficulty connecting to the Internet.

In some cases of spyware infection, the user has no awareness of spyware and assumes that the system performance, stability, and/or connectivity issues relate to hardware, to Microsoft Windows installation problems, or to a virus. Some owners of badly infected systems resort to contacting technical support experts, or even buying an entire new computer system because the existing system "has become too slow." Badly infected systems may require a clean reinstall of all their software in order to restore the system to working order. This can become a time-consuming task, even for experienced users.

Only rarely does a single piece of software render a computer unusable. Rather, a computer rarely has only one infection. As the 2004 AOL study noted, if a computer has any spyware at all, it typically has dozens of different pieces installed. The cumulative effect, and the interactions between spyware components, typically cause the stereotypical symptoms reported by users: a computer which slows to a crawl, overwhelmed by the many parasitic processes running on it. Moreover, some types of spyware disable software firewalls and anti-virus software, and/or reduce browser security settings, thus opening the system to further opportunistic infections, much like an immune deficiency disease. Documented cases have also occurred where a spyware program disabled other spyware programs installed by its competitors.

Some other types of spyware (Targetsoft, for example) modify system files to make themselves harder to remove. (Targetsoft modifies the "Winsock" Windows Sockets files. The deletion of the spyware-infected file "inetadpt.dll" will interrupt normal networking usage.) Unlike users of many other operating systems, a typical Windows user has administrator privileges on the system, mostly for convenience. Because of this, any program which the user runs (intentionally or not) has unrestricted access to the system. Spyware, along with other threats, has led some Windows users to move to other platforms such as Linux or Apple Macintosh, which such malware targets far less frequently.


Many spyware programs reveal themselves visibly by displaying advertisements. Some programs simply display pop-up ads on a regular basis; for instance, one every several minutes, or one when the user opens a new browser window. Others display ads in response to specific sites that the user visits. Spyware operators present this feature as desirable to advertisers, who may buy ad placement in pop-ups displayed when the user visits a particular site. It is also one of the purposes for which spyware programs gather information on user behaviour. Hence, pop-up advertisements lead to some of users' most common complaints about spyware.

Many users complain about irritating or offensive advertisements as well. As with many banner ads, many spyware advertisements use animation or flickering banners which are visually distracting and annoying. Pop-up ads for pornography often display indiscriminately, including when children use the computer (possibly in violation of anti-pornography laws).

A further issue in the case of some spyware programs has to do with the replacement of banner ads on viewed web sites. Spyware that acts as a web proxy or a Browser Helper Object can replace references to a site's own advertisements (which fund the site) with advertisements that instead fund the spyware operator. This cuts into the margins of advertising-funded Web sites.

"Stealware" and affiliate fraud

A few spyware vendors, notably 180 Solutions, have written what the New York Times has dubbed "stealware", and what spyware-researcher Ben Edelman terms affiliate fraud, also known as click fraud. These redirect the payment of affiliate marketing revenues from the legitimate affiliate to the spyware vendor.

Affiliate marketing networks work by tracking users who follow an advertisement from an "affiliate" and subsequently purchase something from the advertised Web site. Online merchants such as eBay and Dell are among the larger companies which use affiliate marketing. In order for affiliate marketing to work, the affiliate places a tag such as a cookie or a session variable on the user's request, which the merchant associates with any purchases made. The affiliate then receives a small commission.

Spyware which attacks affiliate networks does so by placing the spyware operator's affiliate tag on the user's activity—replacing any other tag, if there is one. This harms just about everyone involved in the transaction other than the spyware operator. The user is harmed by having their choices thwarted. A legitimate affiliate is harmed by having their earned income redirected to the spyware operator. Affiliate marketing networks are harmed by the degradation of their reputation. Vendors are harmed by having to pay out affiliate revenues to an "affiliate" who did not earn them through a contractual agreement. [7]

Affiliate fraud is a violation of the terms of service of most affiliate marketing networks. As a result, spyware operators such as 180 Solutions have been terminated from affiliate networks including LinkShare and ShareSale.

Identity theft and fraud

One case has closely associated spyware with identity theft. [8] In August 2005, researchers from security software firm Sunbelt Software believed that the makers of the common CoolWebSearch spyware had used it to transmit "chat sessions, user names, passwords, bank information, etc." [9], but it turned out that "it actually is its own sophisticated criminal little trojan that’s independent of CWS." [10] This case is currently under investigation by the FBI.

Spyware has principally become associated with identity theft in that keyloggers are routinely packaged with spyware. John Bambenek, who researches information security, estimates that identity thieves have stolen over $24 billion US dollars of account information in the United States alone [11].

Spyware-makers may perpetrate another sort of fraud with dialer program spyware: wire fraud. Dialers cause a computer with a modem to dial up a long-distance telephone number instead of the usual ISP. Connecting to these suspicious numbers involves long-distance or overseas charges which invariably result in massive telephone bills that the user is liable for. Dialers are somewhat less effective today, now that fewer Internet users use dialup modems.

Digital rights management

Some copy-protection schemes, while they do serve the purpose of attempting to prevent piracy, also behave similarly to spyware programs. Some digital rights management technologies (such as Sony's XCP) actually use trojan-horse tactics to verify a user as the rightful owner of the media in question.

Sony has been sued for using virus-like techneques to prevent users from copying its CDs. A Rootkit technique was used to embed Sony's software deep inside the Windows operating system to make it hard to find by antispyware software and difficult to uninstall.

Spyware and cookies

Anti-spyware programs often report Web advertisers' HTTP cookies as spyware. Web sites (including advertisers) set cookies — small pieces of data rather than software—to track Web-browsing activity: for instance to maintain a "shopping cart" for an online store or to maintain consistent user settings on a search engine.

Only the Web site that sets a cookie can access it. In the case of cookies associated with advertisements, the user generally does not intend to visit the Web site which sets the cookies, but gets redirected to a cookie-setting third-party site referenced by a banner ad image. Some Web browsers and privacy tools offer to reject cookies from sites other than the one that the user requested.

Advertisers use cookies to track people's browsing among various sites carrying ads from the same firm and thus to build up a marketing profile of the person or family using the computer. For this reason many users object to such cookies, and anti-spyware programs offer to remove them.

Typical examples of spyware

A few examples of common spyware programs may serve to illustrate the diversity of behaviors found in these attacks.

Caveat: As with computer viruses, researchers give names to spyware programs which frequently do not relate to any names that the spyware-writers use. Researchers may group programs into "families" based not on shared program code, but on common behaviours, or by "following the money" of apparent financial or business connections. For instance, a number of the spyware programs distributed by Claria are collectively known as "Gator". Likewise, programs which are frequently installed together may be described as parts of the same spyware package, even if they function separately.

  • CoolWebSearch, a group of programs, installs through the exploitation of Internet Explorer vulnerabilities. The programs direct traffic to advertisements on Web sites including coolwebsearch.com. To this end, they display pop-up ads, rewrite search engine results, and alter the infected computer's hosts file to direct DNS lookups to these sites. [12]
  • Internet Optimizer, also known as DyFuCa, redirects Internet Explorer error pages to advertising. When users follow a broken link or enter an erroneous URL, they see a page of advertisements. However, because password-protected Web sites (HTTP Basic authentication) use the same mechanism as HTTP errors, Internet Optimizer makes it impossible for the user to access password-protected sites. [12]
  • 180 Solutions transmits extensive information to advertisers about the Web sites which users visit. It also alters HTTP requests for affiliate advertisements linked from a Web site, so that the advertisements make unearned profit for the 180 Solutions company. It opens pop-up ads that cover over the Web sites of competing companies. [1]
  • HuntBar, aka WinTools or Adware.Websearch, is a small family of spyware programs distributed by Traffic Syndicate. [12] It is installed by ActiveX drive-by download at affiliate Web sites, or by advertisements displayed by other spyware programs—an example of how spyware can install more spyware. These programs add toolbars to Internet Explorer, track Web browsing behavior, redirect affiliate references, and display advertisements.

User consent and legality

Gaining unauthorised access to a computer is illegal under computer crime laws in several global territories, such as the United States Computer Fraud and Abuse Act. Since the owners of computers infected with spyware generally claim that they never authorised the installation, a prima facie reading would suggest that the promulgation of spyware would count as a criminal act. Law enforcement has often pursued the authors of other malware programs, such as viruses. Nonetheless, few prosecutions of writers of spyware have occurred, and many such producers operate openly as aboveboard businesses. Some have, however, faced lawsuits.

Spyware producers primarily argue in defense of the legality of their acts that, contrary to the users' claims, users do in fact give consent to the installation of their spyware. Spyware that comes bundled with shareware applications may appear, for instance, described in the legalese text of an end-user license agreement (EULA). Many users habitually ignore these purported contracts, but spyware companies such as Claria claim that these demonstrate that users have consented to the installation of their software.

Despite the ubiquity of EULAs and of clickwrap agreements, relatively little case law has resulted from their use. It has been established in most common law jurisdictions that a clickwrap agreements can be a binding contract in certain circumstances. This does not however mean that every clickwrap agreement is a contract or that every term in a clickwrap contract is enforceable. It seems highly likely that many of the purported contract terms presented in clickwrap agreements would be dismissed in most jurisdictions as being contrary to public policy. Many spyware clickwrap agreements appear intentionally ambiguous and excessive in length, with key contract terms made inconspicuous. These are all grounds on which similar agreements have been rejected as contracts of adhesion. In Australia, the proprietors of Sharman Newtorks, who own and operate the KaZaa P2P network were sued by the Australian Recording Industry Association for breaching copyright laws as a result of allowing illegal music to be shared and distributed through the KaZaa network. Sharman Networks claimed that the EULA stated that the program was not to be used for illegal activity, however the claim was dismissed on the grounds that the length and ambiguity of the agreement coupled with the fact that few users read it made the agreement inadmissable as a defence.

Nor can a contract possibly exist in the case of spyware installed by surreptitious means, such as in a drive-by download where the user receives no opportunity to either agree to or refuse the contract terms.

Some jurisdictions, including the U.S. states of Iowa [2] and Washington [3], have passed laws criminalizing some forms of spyware. Such laws make it illegal for anyone other than the owner or operator of a computer to install software that alters Web-browser settings, monitors keystrokes, or disables computer-security software.

New York Attorney General Eliot Spitzer has pursued spyware companies for fraudulent installation of software. [13] In a suit brought in 2005 by Spitzer, the California firm Intermix Media, Inc. ended up settling by agreeing to pay US$7.5 million and to stop distributing spyware. Intermix's spyware spread via drive-by download, and deliberately installed itself in ways that made it difficult to remove. [14]

Another spyware behaviour has attracted lawsuits: the replacement of Web advertisements. In June 2002, a number of large Web publishers sued Claria for replacing advertisements, but settled out of court. Other spyware apart from Claria's also replaces advertisements, thus diverting revenue from the ad-bearing Web site to the spyware author.

One legal issue not yet pursued involves whether courts can hold advertisers responsible for spyware which displays their ads. In many cases, the companies whose advertisements appear in spyware pop-ups do not directly do business with the spyware firm. Rather, the advertised company contracts with an advertising agency, which in turn contracts with an online subcontractor who gets paid by the number of "impressions" or appearances of the advertisement. Some major firms such as Dell Computer and Mercedes-Benz have sacked advertising agencies which have run their ads in spyware. [15]

Some spyware companies have threatened websites which have posted descriptions of their products. In 2003, Gator (now known as Claria) filed suit against the website PC Pitstop for describing the Gator program as "spyware". [16] PC Pitstop settled, agreeing not to use the word "spyware", but continues to publish descriptions of the harmful behaviour of the Gator/Claria software. [4]


Fake anti-spyware programs

Malicious programmers have released a large number of fake anti-spyware programs, and widely distributed Web banner ads now spuriously warn users that their computers have been infected with spyware, directing them to purchase programs which do not actually remove spyware — or worse, may add more spyware of their own. [17] [18]

The recent proliferation of fake or spoofed antivirus products has occasioned some concern. Such products often bill themselves as antispyware, antivirus, or registry cleaners, and sometimes feature popups prompting users to install them. This is called Rogue software.

Known offenders include:

  • Malware Wipe
  • Pest Trap
  • SpyAxe
  • AntiVirus Gold
  • SpywareStrike
  • SpyFalcon
  • WorldAntiSpy
  • WinFixer
  • SpyTrooper
  • Spy Sheriff
  • SpyBan
  • SpyWiper
  • PAL Spyware Remover
  • Spyware Stormer
  • PSGuard
  • AlfaCleaner

For details, please see "Rogue/Suspect Anti-Spyware Products & Web Sites"

On 2006-01-26, Microsoft and the Washington state attorney general filed suit against Secure Computer for its Spyware Cleaner product. [19]


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