Here’s a very good free program that I have been trying out for several weeks now.
Free avast! 4 Home Edition is a free anti-virus software for home noncommercial use. This free virus scanner protects against viruses, worms and Trojans on disk, CDs, in E-mail and during browsing. Incremental updates of virus database (twice a week) are small, fast and reliable.
So far so good and I’m going to recommend it. Now there is no reason to not have a good up-to-date anti-virus program running on your machine. Have a look.