Viruses, (including Malware, Worms, Spyware, Scareware), are programs that are installed without your consent. Many viruses will slow down your computer, interfere with Internet access, send spam emails from your email account, steal your personal information and passwords or damage your computer.
The best defense against viruses is to make sure your anti-virus program is always up-to-date, your firewall is on, and that you use extreme caution when clicking on a link in an email or a website.
If your computer gets infected with a virus, there are two possible routes to removing the virus. The best way (and the only way to be certain that the virus is gone), is to copy all your files, wipe the hard drive clean, Reinstall your operating system and every piece of software, copy your data back, setup printing, Internet access, and email.
The second way, (which works occasionally, depending upon the virus your computer has contracted), is to run several anti-virus tools and hope for the best.