Regarding the recent snippet rampage, it's a mixture of these four facts:
1) A combined effort of ripping off MJ's famous B-team: Brad Buxer, Michael Prince & Brad Sundberg. Basically every song Brad Sundberg has ever played - including "VIP ticket" material - has been secretly recorded with professional devices. Sometimes people even picked off the cables that were connecting the speakers for the audience.
2) There's a collector who has been streaming entire multi-tracks. People were - of course - recording them. Leaks have happened from that. The guy also played some songs. That material is being circulated.
3) There's another collector who did phone calls in which he played stuff. And - of course - people were recording that, too.
4) A combined effort of people that obtained material from #1 - 3, trying to obtain more from other individuals, preferably those who are not aware of #1 -3.