Any software that covertly gathers user information through the user's Internet connection without his or her knowledge, usually for advertising purposes. Spyware applications are typically bundled as a hidden component of freeware or shareware programs that can be downloaded from the Internet. Once installed, the spyware monitors user activity on the Internet and transmits that information in the background to someone else.
Spyware is a broad category of malicious software intended to intercept or take partial control of a computer's operation without the user's informed consent. While the term taken literally suggests software that surreptitiously monitors the user as a spy would, it has come to refer more broadly to software that subverts the computer's operation for the benefit of a third party.
Why is it called spyware?
While this may be a great concept, the downside is that the advertising companies also install additional tracking software on your computer system, which is continuously "calling home", using your Internet connection to report statistical data to the "mothership".
Is spyware illegal?
Even though the name may indicate so, Spyware is not an illegal type of software in any way. However there are certain issues that a privacy oriented user may object to and therefore prefer not to use the product. This usually involves the tracking and sending of data and statistics via a server installed on the user's computer and the use of your Internet connection in the background.
Malicious websites may attempt to install spyware on readers' computers.
The BearShare file-trading program, "supported" by WhenU spyware. In order to install BearShare, users must agree to install "the SAVE! bundle" from WhenU. The installer provides only a tiny window in which to read the lengthy license agreement. Although the installer claims otherwise, the software transmits users' browsing activity to WhenU servers.
Many Internet Explorer add-on toolbars monitor the user's activity. When installed and run without the user's consent, such add-ons count as spyware. Here multiple toolbars (including both spyware and innocuous ones) overwhelm an Internet Explorer session.
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 recommendation. 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:
- System Doctor
- Malware Wipe
- Pest Trap
- SpyAxe
- AntiVirus Gold
- SpywareStrike
- SpyFalcon
- WorldAntiSpy
- WinFixer
- SpyTrooper
- Spy Sheriff
- SpyBan
- SpyWiper
- PAL Spyware Remover
- Spyware Stormer
- PSGuard
- AlfaCleaner
- Spyware Quake
Security practices
To deter spyware, computer users have found a number of techniques useful in addition to installing anti-spyware software.
Many system operators install a web browser other than Microsoft's Internet Explorer (IE), such as Opera or Mozilla Firefox - though such web browsers have also suffered from some security vulnerabilities. Not a single browser ranks as safe, because in the case of spyware the security comes with the person who uses the browser.
Some Internet Service Providers particularly colleges and universities have taken a different approach to blocking spyware: they use their network firewalls and web proxies to block access to Web sites known to install spyware.
Notable programs distributed with spyware
- Messenger Plus! (only if you agree to install their "sponsor" program)
- Bearshare
- Bonzi Buddy
- DAEMON Tools (only if you agree to install their "sponsor" program)
- DivX (except for the paid version, and the "standard" version without the encoder). DivX announced removal of GAIN software from version 5.2.
- Dope Wars
- ErrorGuard
- FlashGet (free version)
- Grokster
- Kazaa
- Morpheus
- RadLight
- WeatherBug
- EDonkey2000
As the spyware threat has worsened, a number of techniques have emerged to counteract it. These include programs designed to remove or to block spyware, as well as various user practices which reduce the chance of getting spyware on a system.
Nonetheless, spyware remains a costly problem. When a large number of pieces of spyware have infected a Windows computer, the only remedy may involve backing up user data, and fully reinstalling the operating system.
Programs to use, in case spyware does in fact impact your computer
- Ad-Aware
- Spybot S+D
- Spyware Doctor
- Webroot Spysweeper
- HijackThis
You could also just check www.download.com, they have some great security tips!