Originally Posted by Quentin

Yes, ISPs have provided information on users who have allegedly uploaded infringing materials. Under the DMCA, once served with a proper subpoena, the ISP has no real choice other than to fork over any identifying information that they have on such users.

Here's the text of the relevant section of code (which is 17 USC §512(h), for those keeping score at home):



To not respond to such a subpoena would probably not be the best business decision an ISP can make. The courts usually aren't particularly amused by that sort of thing.