First of all, you don't need any of that. As a rule of thumb, just ignore anything below 1-2 megabytes (unless you're looking for pictures or the like). Apparently some people really don't know how much a kilobyte, megabyte etc. is and download incredibly small files assuming it's gonna be the video or software they were looking for. Or maybe they just don't look at the size at all.

The spammers can and do modify their little nasty files regularly. It's unlikely that you could keep a database of those up-to-date with reasonable effort. Also whether these are viruses or not is really not important. The existence of these search results themselves is a far worse problem especially because it harms also those users which are rather smart. The amount of search results you get is limited and the more spam there is, the less good results are you going to get.

This gets us to the next point: Yes, it can hurt. If you share "crap" with the names of files people are looking for this means the results delivered by your peer will reduce the number of useful resuls these people may get. One person doing this is hardly a problem but it's really no help either.

What you could do, is creating a bitzi ticket for any bad file so that people get a warning when they bother to lookup
a file before downloading it. However, there's so much spam and there'll probably be a lot more in the future that Bitzi
cannot be expected to scale for this purpose. The amount of good files is virtually limited, the amount of useless or bad data is infinite. One should also keep in mind that anyone can submit whatever he wants to Bitzi so you could claim spam is good content and vice-versa.

If you actually create a bitzi ticket for some spam file, make sure you clear the filename because - as explained - the filename is useless and would be misleading. Certain spam can be recognized by filename patterns but that's really something else.