Check the newest security tip by US-CERT entitled Recovering from Viruses, Worms, and Trojan Horses
“Unfortunately, many users are victims of viruses, worms, or Trojan horses. If your computer gets infected with malicious code, there are steps you can take to recover.“
How do you know your computer is infected?
What can you do if you are infected?
How can you reduce the risk of another infection?
Read the complete security tip in http://www.us-cert.gov/cas/tips/ST05-006.html