Smooth criminals who hacked into Sony Music's servers last year may have made off with 50,000 music files consisting of the late Michael Jackson's entire back catalog, including many unreleased tracks, according to a report that appeared March 3 on the website of the Sunday Times of London.

"Everything Sony purchased from the Michael Jackson estate was compromised," an unnamed source told the newspaper. "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."

Sony Music Entertainment confirmed to the BBC on March 5 that there had been a security breach, but would not confirm if anything had been stolen. Most of the 50,000 compromised files alleged by the Sunday Times would probably be snippets of music or individual instrument or vocal tracks instead of release-ready songs.

A system breach wouldn't automatically mean theft; to know for certain, Sony would have to check its network traffic logs for signs of a large amount of outgoing data.

However, the Sunday Times said Sony had launched an internal investigation after reading rumors of a theft on Jackson fan websites and in hacking chat rooms.

The material that may have been stolen was said to have included duets with Black Eyed Peas singer Will.I.Am and with Freddie Mercury, the lead singer of Queen who died of AIDS in 1991.

Sony's PlayStation Network and two other private networks belonging to the company were breached in April 2011, resulting in the compromise of more than 100 million user accounts. Other Sony online properties were also attacked last year. It is not clear if the Jackson data breach was connected to a previously known attack.

Two men apparently connected to the Jackson incident appeared in court on March 2 in Leicester, central England, facing charges of computer hacking and copyright infringement. Both men, who had originally been arrested in May 2011, pleaded not guilty. A court date was set for January 2013.

Because the data breach involved no personal data belonging to private citizens, Sony was under no obligation to reveal it until the court appearance.

Nine months after Jackson died in June 2009, Sony Music Entertainment, which had a long-standing business relationship with the singer, obtained the rights to Jackson's entire back catalog for $250 million. One album of previously unreleased tracks was released in late 2010.

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