Sony Corp. has announced that its PlayStation Network services will resume in stages over the coming days and it is planning to "welcome back" users with an unprecedented giveaway of free downloads and access to premium games and music.

The Japanese electronics giant has been criticized in some quarters for failing to respond more quickly after a breach of security by hackers gave them access to some 77 million accounts.

The company held a press conference in Tokyo on Sunday in which senior officials apologized for the intrusion into users' accounts. The company used the occasion to announce new security measures and vow to track down the hackers responsible, but the most popular measure appears to have been the offer of freebies.

"The company will also roll out the PlayStation Network and Qriocity 'Welcome Back' programme, to be offered worldwide, which will be tailored to specific markets to provide our consumers with a selection of service options and premium content as an expression of the company's appreciation for their patience, support and continued loyalty," Patrick Seybold, senior director of corporate communications, said in a statement.

The freebies will vary from territory to territory, with the details of what will be available to be announced in the near future, the company said, while all existing PlayStation Network customers will be given 30 days' free membership to the PlayStation Plus premium service. Current members of the scheme will receive 30 days' free service.

In addition, users of Music Unlimited powered by Qriocity will receive 30 days' free access.

The company has also promised to roll out further services over the coming weeks as it returns "to the quality standard users have grown to enjoy."

Before the system goes live again, Sony will reinforce and verify its security for transactions, but the company on Monday called on its users to change their passwords.

Some people are still not satisfied with Sony's efforts, however, with a user in Alabama filing a class-action suit for all those affected and demanding reimbursement for any losses due to credit card data theft, refunds for services that are defective and punitive damages.

Sony has asked the FBI to investigate the security breach and it is also working with law enforcement authorities in Britain, Australia and Hong Kong to identify the hackers.