Spyware, virus and worm

Unlike viruses and worms, spyware does not generally self-replicate. Like many recent viruses, however, spyware — by design — exploits impure computers for commercial gain. Typical tactics furthering this goal contain delivery of unsolicited pop-up advertisements; theft of personal information (including financial information such as credit card numbers); monitoring of Web-browsing action for marketing purposes; or routing of HTTP requests to advertising sites.