Looking for an open source antivirus..? Clamwin antivirus is the best open source antivirus software available right now.
Clamwin antivirus is a free software available for all versions of Windows operating system. Yes it does support Windows 7.
Good thing about Clamwin when compared to other open source anti virus is that it has been regularly getting updates. This is mainly because of its 600,000 odd users. You can also pitch in with your support for the development of this tool. You can download its source code from their main site.