Upload hook, antivirus software

I want all user uploads being run through anti-virus software. My hosting company offers the software. All I have to do, is to run the uploads in /tmp through it right after they have been uploaded via a shell_exec in PHP and to delete the uploaded file rather than move it to the uploads directory if the upload string contains "Infected". However, I don't want to put this into upload.module since I'd have to change upload.module after every update of the module or of Drupal. I want to put it in a module on its own.

What hook would you use? Anything you can hint me at? Any suggestions?