TOKYO - Sony executives bowed in apology Sunday for a security breach in the company's PlayStation Network that caused the loss of personal data of some 78 million accounts on the online service, and promised free help to customers.

"We deeply apologize for the inconvenience we have caused," said Kazuo Hirai, chief of Sony Corp.'s PlayStation video game unit, who was among the three executives who bowed for several seconds at the company's Tokyo headquarters in the traditional style of a Japanese apology.

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Hirai said parts of the service would be back this week and that the company would beef up security measures.

He said the FBI and other authorities had been contacted to start an investigation into what the company called "a criminal cyber attack" on Sony's data center in San Diego, California.

Sony said account information, including names, birth dates, email addresses and log-in information, was compromised for players using its PlayStation Network. Hirai asked all users to change their passwords.

Hirai reiterated what the company said last week - that even though it had no direct evidence the data were even taken, it cannot rule out the possibility.

He said data from 10 million credit cards were believed to be involved, and that Sony still does not know whether information was stolen.

Sony has added software monitoring and enhanced data protection and encryption as new security measures, he said. The company said it would offer "welcome back" freebies such as complimentary downloads and 30 days of free service around the world to show remorse and appreciation.

The network, which serves both the PlayStation video game machines and Sony's Qriocity movie and music services, has been shut down since April 20. It is a system that links gamers worldwide in live play, and also allows users to upgrade and download games and other content.

Hirai said Sony suspected it was under attack by hackers starting April 17.

According to Sony, of the 78 million PlayStation Network accounts, about 36 million are in the US and elsewhere in the Americas, while 32 million are in Europe and 9 million in Asia, mostly in Japan.

Pressure is mounting on Sony to restore services and compensate players.

US lawmakers have sent a letter to Hirai demanding answers by May 6 about the security breach and Sony's response.

Hirai said he had read the online version of the letter and would answer the questions as soon as possible.

Last month, US lawyers filed a lawsuit against Sony on behalf of lead plaintiff Kristopher Johns for negligent protection of personal data and failure to inform players in a timely fashion that their credit card information may have been stolen. The lawsuit seeks class-action status.