well it sounds like you're just being spoofed via one of the leased plugins - how any plugin companies are still using referer method is beyond me.
are you seeing a spike in the numbers of your own files in the members area being downloaded? if not then no doubt it's just simple spoofing to get into the plugins.
whick company leases these feeds
http://www.revengetv.com/chop1/index2.php ?