Lavasoft’s Ad-Aware, one of a few reliable commercial anti-spyware programs, scans the hard drive of a clean Windows XP system.
Many programmers and some commercial firms have released products designed to remove or block spyware. Steve Gibson’s OptOut, mentioned above, pioneered a growing category. Programs such as Lavasoft’s Ad-Aware SE and Patrick Kolla’s Spybot – Search & Destroy rapidly gained popularity as effective tools to remove, and in some cases intercept, spyware programs. More recently Microsoft acquired the GIANT Anti-Spyware software, rebadging it as Windows AntiSpyware beta and releasing it as a free download for Windows XP, Windows 2000, and Windows 2003 users. In early spring, 2006, Microsoft renamed the beta software to as “Windows Defender”, currently “beta 2.” The renamed software for now exists as a time-limited beta test product that will expire (beta 1 in July 2006, and beta 2 in December, 2006). Microsoft has also announced that the product will ship (for free) with Windows Vista. Other well-known anti-spyware products include Webroot Spy Sweeper, PC Tools’ Spyware Doctor, ParetoLogic’s XoftSpy, and Sunbelt’s CounterSpy (which uses a forked codebase from the GIANT Anti-Spyware product).
Major anti-virus firms such as Symantec, McAfee and Sophos have come later to the table, adding anti-spyware features to their existing anti-virus products. Early on, anti-virus firms expressed reluctance to add anti-spyware functions, citing lawsuits brought by spyware authors against the authors of web sites and programs which described their products as “spyware”. However, recent versions of these major firms’ home and business anti-virus products do include anti-spyware functions, albeit treated differently from viruses. Symantec Anti-Virus, for instance, categorizes spyware programs as “extended threats” and now offers real-time protection from them (as it does for viruses).
Real-time protection blocks spyware in the process of installing itself. Here, Windows AntiSpyware blocks an instance of the AlwaysUpdateNews spyware.
Anti-spyware programs can combat spyware in two ways:
- real-time protection, which prevents the installation of spyware
- detection and removal of spyware.
Writers of anti-spyware programs usually find detection and removal simpler, and many more programs have become available which do so. Such programs inspect the contents of the Windows registry, the operating system files, and installed programs, and remove files and entries which match a list of known spyware components. Real-time protection from spyware works identically to real-time anti-virus protection: the software scans incoming network data and disk files at download time, and blocks the activity of components known to represent spyware. In some cases, it may also intercept attempts to install start-up items or to modify browser settings.
Earlier versions of anti-spyware programs focused chiefly on detection and removal. Javacool Software’s SpywareBlaster, one of the first to offer real-time protection, blocked the installation of ActiveX-based and other spyware programs. To date, other programs such as Ad-Aware and Windows AntiSpyware now combine the two approaches, while SpywareBlaster remains focused on real-time protection.
Like most anti-virus software, many anti-spyware/adware tools require a frequently-updated database of threats. As new spyware programs are released, anti-spyware developers discover and evaluate them, making “signatures” or “definitions” which allow the software to detect and remove the spyware. As a result, anti-spyware software is of limited usefulness without a regular source of updates. Some vendors provide a subscription-based update service, while others provide updates gratis. Updates may be installed automatically on a schedule or before doing a scan, or may be done manually. Not all programs rely on updated definitions. Some programs rely partly (for instance Windows Defender) or entirely (BillP’s WinPatrol, and certainly others) on historical observation. They watch certain configuration parameters (such as the Windows registry or browser configuration) and report any change to the user, without judgment or recomendation. Their chief advantage is that they do not rely on updated definitions. Even with a subscription, a “critical mass” of other users have to have, and report a problem before the new definition is characterized and propagated. The disadvantage is that they can offer no guidance. The user is left to determine “what did I just do, and is this configuration change appropriate?”
If a spyware program is not blocked and manages to get itself installed, it may resist attempts to terminate or uninstall it. Some programs work in pairs: when an anti-spyware scanner (or the user) terminates one running process, the other one respawns the killed program. Likewise, some spyware will detect attempts to remove registry keys and immediately add them again. Usually, booting the infected computer in safe mode allows an anti-spyware program a better chance of removing persistent spyware.
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.  
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.
Known offenders include:
PAL Spyware Remover
On 2006-01-26, Microsoft and the Washington state attorney general filed suit against Secure Computer for its Spyware Cleaner product. 
- ↑ Roberts, Paul F. “Spyware-Removal Program Tagged as a Trap“. eWeek. May 26, 2005.
- ↑ Howes, Eric L. “The Spyware Warrior List of Rogue/Suspect Anti-Spyware Products & Web Sites“. Retrieved July 10, 2005.