Signs of a spyware

• Unauthorized pop-up advertisements,even when not browsing the Web
• A change to the browser home page order, search engine without user consent, which often resists attempts to change it back
• A new and unwanted toolbar on the browser, which often resists attempts to remove it
• A sudden and dramatic slowdown in PC performance
• Increased crashing of operating systems, Web browsers, and other common applications

  Spyware covers a broad category of malicious software designed to intercept or take partial control of a computers operation or collect personal information without the informed consent of that machines owner . Spyware programs perform actions such as displaying advertising,tracking Web sites visited, or changing the configuration of a PC.
Spyware differs from viruses and worms in that it does not usually self-replicate. Like 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 requests to advertising sites.

History and Development

The first recorded use of the term spyware occurred on October 16, 1995 in a Usenet post that poked fun at Microsoft’s business model. 1999 saw the introduction of the first popular freeware program to include built-in spyware: humorous and popular game called Elf Bowling spread across the Internet in November 1999, and many users learned with surprise that the program actually transmitted user information back to the games creator, Nsoft
According to an October 2004 study by America Online and the NationalCyber-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 it to be installed
  As of 2005, pundits have often characterized spyware as the pre-eminent security threat for computers running Microsoft Windows operating systems. Some malware on the Linux and Mac OS X platforms has behavior similar to Windows spyware.