hmm interesting find. Here's two techniques to know good from bad files; audio files that are good & ones that are drm infested or simply spammed bad files.
(1) File size is often a common denominator. Virus thread: Typical virus spam file sizes - Make a note of them (click on blue link to see). Especially the last image.

(2) Bitrate. (a) The files that show no bit rate are generally not real audio files. (b) The files that do not have an appropriate bit rate according to file size & length of song are deliberately corrupted audio files. eg: You might find a song that runs for 3 mins. with a bit rate of 192 kbps & file size of 3.5 MB. You might find another that runs for 3 mins with a bit rate of 320 & also has same file size. Chances are one of them is a bad file. mp3 Bit-Rates Versus File Sizes (click on link)