If you know you PC is infected with malware, you'll need a program like McAfee Labs Stinger. This free tool targets worms, trojans and viruses already lurking on your computer, then rapidly destroys them to leave your PC infection-free once more.
Why you need it
Why would you need McAfee Stinger when your own antivirus software already exterminates threats?
Cleans up existing infections
Detects zero-day threats
Easy to use
Well, Stinger is a much more targeted tool, searching in the registry and directories that viruses use to avoid the long scans performed by your antivirus program. That means Stinger can find threats that your regular software may well miss.
There's no installation required, just double click on the EXE file to load up McAfee Labs Stinger. That makes it ideal for when you need to eliminate a threat as quickly as possible.
Note that McAfee Labs Stinger isn't a replacement for your normal virus scanner, and you should use a tool with real-time protection to pick up any threats before they damage your system. It's a real life-saver in an emergency though, and well worth keeping on a USB stick in case the worst happens.