Sony said it would start Sunday a “phased restoration” of network services that came under hacker attacks in one of the biggest data breaches since the advent of the Internet.

The cyber attacks in recent weeks involved the theft of personal data that include names, passwords and addresses from more than 100 million accounts on its PlayStation Network and Sony Online Entertainment services.

Sony has said it cannot rule out that millions of credit card numbers may have been compromised.

The entertainment and electronics giant said it would resume PlayStation Network and Qriocity services in phases, with full restoration expected by the end of the month.

“The phased restoration will be on a country-by-country basis beginning in the Americas, Europe, Australia, New Zealand, and Middle East,” the Sony group said in a statement. Services in other areas would follow.

“Working closely with several respected outside security firms, the company has implemented new and additional security measures that strengthen safeguards against unauthorised activity, and provide consumers with greater protection of their personal information,” Sony said.

Sony shut down the PlayStation Network and Qriocity services on April 20 after a cyber attack on the company’s data centre in San Diego.

“We are taking aggressive action at all levels to address the concerns that were raised by this incident, and are making consumer data protection a full-time, company-wide commitment,” said Kazuo Hirai, Sony executive deputy president.