AVG 6.0 is Free for Non-Commercial Use:
[link|http://www.grisoft.com/|http://www.grisoft.com/]
NAV sometimes lets viruses slip by, or so others have told me after they switched to AVG AV.
Could be a Trojan too, try The Cleaner for 30 days:
[link|http://www.moosoft.com/thecleaner/download.php|http://www.moosoft.c...aner/download.php]
I liked it so much that I registered it. The 30 day demo helped clean up a friend's system that did file sharing. Beware of stuff you get from file-sharing networks, they are unverified and may contain trojan or virus code.