The April 2011 hack on Sony’s PlayStation Network and Qriocity (now known as Sony Entertainment Network Music Unlimited) not only left PSN subscribers without service for a month, but hackers may have also stolen some 50,000 music files, most of which are from the King of Pop, Michael Jackson.

Back in 2010, after the death of Jackson, Sony Entertainment paid $250 million for the Jackson estate which includes every song the King of Pop ever recorded.  The hackers reportedly stole Jackson’s entire catalog and some unreleased tracks, including duets with Will.I.Am and Freddie Mercury.

“Everything Sony purchased from the Michael Jackson estate was compromised,” said the unnamed source.  “It caused them to check their systems and they found the breach. There was a degree of sophistication. Sony identified the weakness and plugged the gap.”

The deal also entitled Sony to use Jackson’s music in computer games, television ads and elsewhere, with profits from the arrangement to go into a trust shared by the singer’s mother and three children.

Sony Music houses major artists including Leonard Cohen, Paul Simon, Foo Fighters and Avril Lavigne, and they also distribute the music of Jimi Hendrix.

Sony has yet to confirm or comment on the issue.

On a related note, the two men arrested back in May 2011 for the PSN breach, James Marks from Daventry in Northamptonshire, and James McCormick from Blackpool, appeared in court last Friday, and denied charges under the Computer Misuse Act and the Copyright, Designs and Patents Act at Leicester crown court. The two are now out on bail and will stand trial on January 2013.