A _very_ hard time, since the de-CSS implementation in use by most software is not derived from code owned by the MPAA. Copyright is not at issue here. The algorithm is not patented either. The MPAA could, however, make a claim under the DMCA that the software is designed to circumvent a technological protection. That line of reasoning will only hold up in America though. The rest of the world is not (yet) so beholden to the media corporations that they sabotage their copyright laws to support this kind of run around consumer rights.

Ironically, breaking the CSS scrambling is not required to copy DVD’s – only to play them. It was added to content to force player manufacturers to pay royalties, not to protect the content. This transparent imposition of monopoly rights is ignored by almost all open source software, who believe (with reasonable justification, in my opinion) that legally acquired digital content can be manipulated in any the user wants (including descrambling it to view it on the hardware of their choice).