First, do some research on your target. That site also provides you with a tool to clean it up.
Here's another source of information and instructions for clean up.
For more information on this topic, visit these other SearchSecurity resources:
Virus Prevention Tip: Cleaning out a virus infection
News & Analysis: New Klez variant can cause some damage
News & Analysis: Rise and shine for Klez-E
This was first published in April 2002