Well they can slap "copyrighted" on anything these days. The way the U.S. Copyright laws work, everything is copyrighted the moment it is written and doesn't need to be filed or anything. (including things as simple as emails). Problem is proving it was yours first without filing it.
On the other hand, they have to prove they suffered some sort of loss from what you did in some cases. So lutherberry said, prepare to write a big check or come up with some other compromise. Or whatever it is you downloaded, if you didn't upload anything, you could always try buying whatever it was they're trying to slap you with and scratch it up, play dumb and say you were trying to repair the disk with the new file. (I know it makes no sense to you, but to many not-so-tech-savy people it would
)
also I don't take responsibility for my stupid farfetched idea.