They definitely can't scan for and delete files on any criterion. If they could, they'd be forced to use it on mp3s by the RIAA and such, and the network would generally be susceptible to coercive censorship, something it was designed to resist.

OTOH, they could make file Bitzi ratings, or detected virus signatures, or similar information visible in the UI in the search results and let users decide whether or not to download the file...