These spams don't just come from spurious search results. Sometimes one gets legitimate search results (i.e. they are not from a T1 source, have only one or a handful of sources, and the filename isn't a simple derivative of your query) but downloading them results in a spam. It looks like the download "mesh" gets polluted too, and when you try to download a file from a "real" search result, sometimes a spammer gets in at that point and substitutes junk.

If Limewire sent hashes with search results and checked files against search result hashes it would catch these with "File corrupted", but it doesn't -- and lots of other broken files don't get detected either. Looks like it trusts the host sending the file to be honest about the hash and the file.