No reason to suspect it's not genuine, MB, You have to be VERY careful what you download off Limewire (or similar), as the networks are rife with nasties. However, you usually have to download and run an .exe file, to actually activate the virus, and any good anti-virus / anti-spyware software should have spotted this, so I would suggest a lesson in computer security might be in order for Michael. He should scan EVERYTHING, and I mean EVERYTHING he downloads off Limewire, for viruses and spyware. He should also check the file sizes of things before downloading them. If, for example, he wants to download a program which he knows is, say, roughly 20Mb, and finds lots listed at 851kb, these are not going to be the genuine thing, but probably a trojan of some sort. MP3s are usually quite safe, but should still be scanned before opening.
Just one other thing, is this Limewire, or Limewire Pro? I have heard of people looking a free download of the Pro version, on warez or torrent sites, and found some of these to contain a trojan.