Vanishing Files

[NedDeRed]

Anyone any idea what is going on? Most of the files in my shared folders, 90 gb worth, suddenly vanished. A few folders also vanished but most remained intact. However, instead of the mp3 files they should contain sone of them had pics of obscure album covers - not one's I had in my collection. The pattern of disappearance appeared to be connected to dc++ downloads in that some of the most recent downloads were still there - but I'm not certain about this. I managed to undelete about a half of the files but the rest are gone forever. Luckilyabout 90% were in a back-up.
How can thousands of files all vanish when the directory structure is nearly intact and there were no errors detected by scan-disk???
Is there a weird DC++ virus?