Avast offer a real-time scanning on P2P.

it how it work, while downloading, Avast will scan the file to make sure if no trace of virus, and will scan again later. after the download, Avast scan again to still to make sure no virus. they supported popular p2p program, but they dont have a support for Phex and FrostWare, because it new.

And it wont lag your download while scan, it just a quick scanning in the background