There's a new patch to the Red Hat Linux Kernel. However, if you're a US citizen or under US jursidiction, you cannot be told what the patch actually doees. According to this Register story, due to restrictions of the DMCA, the patch cannot be explained to US citizens w/o violating the DMCA. It's intended as an exercise to show how the DMCA can restrict the flow of information in the US (theoretically to "protect" the rights of copyright holders).