Unlike viruses and worms

Unlike viruses and worms, spyware 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