Almost all files less than 2 MB are not good. Except for images & some low bit rate audio files.

The above sizes have been recognised by users as being spam which are either viruses or something unpleasant or fake.

It's good you have taken a note of those sizes. Now for music your main concern will only be mp3 Bit-Rates Versus File Sizes (click on link) which again, is something you learn bit by bit. If you see files of same bitrate but very different sizes & the audio length of the song is the same or similar then you know something is wrong with at least one of them.

Use these tips too http://www.gnutellaforums.com/downlo...wire-spam.html