The companies behind an encryption system for high-definition DVDs are looking into a hacker's claim that he has <A HREF="http://www.eweek.com/article2/0,1895,2077999,00.asp?kc=EWNAVEMNL010207EOAD">cracked the code</A> protecting the new discs from piracy. A hacker known as Muslix64 posted on the Internet details of how he unlocked the encryption, known as the Advanced Access Content System, which prevents high-definition discs from illegal copying by restricting which devices can play them.