The antivirus plugin allows you to have the system check each uploaded file to be checked against an antivirus software. If the file is decidedly viewed as a potential virus, then it is marked as such and download are then forbidden.

When the plugin is installed, it prevents all downloads from anyone except the person who uploaded the file until the file gets checked.

Although this will not prevent a certain number of files with viruses to be uploaded and offered for download, it certainly will reduce the amount of such problems in the long run.