I searched around a little bit, since I found the lack of details somewhat disturbing. This is the best I found: http://www.seattlepi.com/news/article/Facebook-hack-lands-UK.... From the sounds of it, he broke into an employees account (likely their work computer, possibly further access). I'm speculating, but that makes it sound like he stole some portion of the Facebook source code, coupling that with the "intellectual property" claims.

I'm curious about this line, towards the bottom:

   his intention throughout was to contact Facebook in due course when he had rectified their problems