Have you recently downloaded any software over the Internet? Your computer may be infected with spyware. Freeware and shareware programs downloaded over the Internet are the most common sources of spyware. Peer-to-peer file-sharing programs are especially notorious for including spyware in their downloads.
You may have spyware on your system if:
Your computer performance has slowed dramatically
While viewing a Web site, other instances of your browser open and display advertisements
Pornographic sites keep popping up when you surf the Internet
Your computer dials phone numbers in the middle of the night to expensive pornographic chat lines, or makes long distance or international calls
New toolbars are unexpectedly added to your Web browser
You get pop-up advertisements that use your name even when you aren't connected to the Internet
Your Web browser suddenly closes and stops responding
Your Internet home page changes
New Web sites are added to your Favorites list
You should remove the spyware as soon as possible to protect your privacy and improve the performance of your computer.