It may be a rogue antivirus program. I suggest contacting support for help with removal. How to reach support -
http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/30400b52-7f26-4ba0-bc18-17e305329d90
Jim
Microsoft MVP Consumer Security - Forum Moderator - Live One Care - Live Mesh - Microsoft Security Essentials