More than 50,000 music files, most of which were by the late pop legend, are said to have been illegally downloaded.
Jackson's estate signed the biggest recording deal in history, worth $250m (£164m) with the company in 2010, giving it the rights to sell his whole back catalogue as well as previously unreleased tracks.
On Friday, two men who were arrested last May appeared in court in the UK accused of offences in connection with the alleged security breach.
James Marks, 26, from Daventry in Northamptonshire, and James McCormick, 25, from Blackpool, denied charges under the Computer Misuse Act and the Copyright, Designs and Patents Act at Leicester crown court. They were released on bail, the Serious Organised Crime Agency said. They are due to stand trial next January.
The incident comes less than a year after the names, addresses and other personal data of about 77 million people with accounts on Sony's PlayStation Network (PSN) were stolen.
The company warned it had been hacked last April when an "illegal and unauthorised person" got access to the information, forcing Sony to temporarily shut down the PSN, which allows owners of the consoles to play online games and rent films.
Private investigators were called in and Sony issued an apology for the "frustrating" security breach, promising it was taking steps to make its services "safer and more secure than ever before" in the wake of the attack.
Sony Music declined to comment on the latest alleged hacking incident. I also heard that Sony has paid $250 million to the Jackson estate.
