Good to hear you are not a spammer and that you found some ideas in the threads here about using the junk filter and side bar filter to help avoid the spam.

Another suggestion is to look at the file size: a .dmg for a true OS X program is already compressed, so a zipped file should be almost the same size as the .dmg. Most of the virus files will be way too small.

Another way I use to avoid spam hosts is to do a garbage search using the "any type" search, and mark all the results as junk. For example, try searching for "eye catcher .dmg" As you know, there is probably no such file, so all the results that come back are coming from spammers. After a while LW will learn which files to mark as junk.

Too, a third way to help avoid spam results is to use the "connections" pane (you can turn it on from LW's View menu). So, when one of my "garbage" searches instantly gets 400+ results, I know I'm connected to some bad hosts that show in the connections. When this happens, try to guess which hosts in connections are bad, and remove them. Try the search again. Good hosts don't instantly return garbage results.

Best wishes.