There are a wide variety of viruses out there that can do all kinds of damage to your computer from causing simple annoyances to destroying your data. No antivirus program is 100% effective and sometimes you have to resort to specialized tools to rid your computer of certain viruses. McAfee has been in the antivirus game for quite some time and has a decent antivirus program that you can buy but they also offer some free help as well.
McAfee offers a collection of tools that can be used to perform tasks that are not commonly encountered during typical use of their antivirus products. Each tool was designed to solve problems caused by viruses or Trojans or to be used for data gathering for analysis of virus caused damage. If you are fortunate enough to know what virus infection you have on your computer and McAfee makes a tool for that infection then its a great way to clean the virus off of your computer.
Some examples of the viruses these tools can clean include:
Sasser, Bagle, Zafi, Mydoom, Lovsan/Blaster, Klez, Bugbear
Check out the McAfee tools page for more details and for links to download these virus removal tools.