Free Online Scans
Microsoft Security Essentials
Microsoft Security Essentials provides real-time protection for your home PC that guards against viruses, spyware, and other malicious software.
Microsoft Security Essentials is a free (for Windows Genuine Advantage users) download from Microsoft that is simple to install, easy to use, and always kept up to date so you can be assured your PC is protected by the latest technology. It’s easy to tell if your PC is secure — when you’re green, you’re good. It’s that simple.
ShieldsUP! is a free security scanner from Gibson Research Corporation designed to test your computer's vulnerability to online threats. Running ShieldsUP! and following up on any warnings it may issue should help to protect you and your computer from common threats.