Which thread was deleted? As for approving each file I've made sure to check the md5 of each the attachment and the VS's as well running a Nod32 scan as well as a few others we have at our disposal.
As for the deletion of threads I delete threads if there are multiples of the same thread by on person, it is a spam thread (with advertising or completely pointless information), or if it breaks any of the major rules. I close inactive threads, threads that are bumped with spam from people other than to whom the thread concerns, if a hack is patched, etc.
Basically if I see a surplus of threads that are breaking the rules I will not hesitate to delete them, we delete many treads on a daily basis just to keep the section looking nice. If we simply closed them all you wild still see the advertisements and the mess we clean up each day.
PM me if you want to talk about this more.