The problem: You contract a virus on your journeys across the Web.
The fix: To prevent infecting other computers on your network, turn off the network discovery function as well as file and printer sharing. Next, right click on your network icon and choose “disable,” or, if you own a Mac, just unplug the Ethernet cable in the back. Also, try running the latest updates for Windows or OS X. While this won’t eliminate the virus, it will neutralize it so it won’t continue to spread. Update your anti-virus software and run a full system scan to eliminate the intruding software. If you own a Mac, try out ClamXav to prevent Mac-specific malware.
As a last resort, since you may lose some files, reinstall your operating system (OS) with the installation disks that came with your computer. Another available route, if you can’t remove spyware from your computer with the normal virus removal tool, is to go into System Restore, turn it off, and then run the virus scan. Sometimes files can get embedded in the restore point, so, if you turn it off, you can remove the virus. Be sure to turn it back on once the virus is removed.