TOKYO - Sony executives bowed in apology Sunday for a security breach in the company's PlayStation Network that compromised the personal data of about 77 million accounts on the online service.

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

Hirai said that parts of the service would be back this week and that the company would beef up security measures. But he and other executives acknowledged that not enough had been done in security precautions, and promised that the company's network services were under a basic review to prevent a recurrence.

Hirai 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.

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

He 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 that 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.

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