Popular torrent search-engine Torrentspyclosed its doors to US visitors Sunday in advance of a court order compelling it to begin logging users' IP addresses. Torrentspy doesn't host infringing files itself, but it does host the .torrent files that contain information pointing to torrent trackers, which connect users to other users sharing the same file. (I'm taking Copyright this semester, so in a few months I'll tell you whether the torrent files are even infringing.) The MPAA sued several torrent sites for copyright infringement earlier this year, and as part of discovery requested the site's server logs.
Discovery is a unique part of the US legal process whereby the parties to a lawsuit get to force each other to turn over information relevant to the case. The scope of discovery is pretty broad, and parties can be sanctioned for destroying evidence or refusing to respond to discovery requests. Generally, though, you can only be compelled to turn over information you already have – not create new documents or information solely for the benefit of the other side.
The original magistrate judge's order, which had been stayed pending appeal, was upheld by the District Court and will take effect. Torrentspy says it plans to appeal the decision, but in the meantime searches originating from US IP addresses get shunted to a page titled "Torrentspy Acts to Protect Privacy", where the site explains its decision as a response to the “uncertain legal climate in the US regarding user privacy.”