if you have formatted your c: drive, the situation u describe is impossible.
impossible is nothing... to begin with
if anyone does not believe me, just take the time and make your own conclusions and don't treat me as if I was dumb-stupid, I know what I say. At this point I believe the only way they ARE doing this is by grabbing (somehow with actionscript or maybe a hidden script on another web scripting languaje) some hardware unique id's, like the cpu one or the hard disk one, or maube a combination of both.
by the way, I always zero all data when formatting.