Sony chief Howard Stringer has warned he can no longer guarantee the security of the electronics giant's gaming network in the "bad new world" of cybercrime after one of the biggest Internet data breaches.

The Japanese multinational has begun restoring its hacked PlayStation Network and Sony Online Entertainment services after the theft of personal data from more than 100 million accounts in a cyber attack estimated to have cost the firm $1 billion.

The company has bolstered security but Stringer, speaking for the first time on the crisis Tuesday, said protecting private information was a "never-ending process" and he did not know if anyone could be "100 percent secure".

Sony shut down the PlayStation Network and Qriocity music streaming service on April 20 after its data centre in San Diego was hacked -- but it did not reveal the breach until April 26.

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

Stringer, 69, warned hackers may one day target the global financial system, the power grid or air-traffic control systems.

"It's the beginning, unfortunately, or the shape of things to come," he told Dow Jones Newswires. "It's not a brave new world -- it's a bad new world."

The breach is a huge blow for Sony as it focuses on pushing content such as games and music through hardware platforms including game consoles, smartphones and tablet computers amid competition from Apple's iTunes and App Store.

Sony was lashed by bitter criticism over the crisis which overshadowed the earnings bounce-back made by the firm after two years of losses.

Stringer hit back at politicians and Internet privacy advocates who said Sony should have alerted subscribers to the threat of a possible data theft sooner.

He said Sony did not know conclusively until April 25 that personal information had been accessed and added that said talking publicly about the company's suspicions before gathering evidence would have been "irresponsible".

"We were trying to find out in a very volatile situation what had happened and when we did we relayed it," said Stringer. "If your house has been burglarised, you find out if you've lost something before you call the police," he said.

Stringer said the Federal Bureau of Investigation probe into the matter was still ongoing but declined to provide an update on the findings.

The CEO said it was too early to assess the financial impact of the outage, with the company reporting its full-year results on May 26, but analysts estimate the breach will cost the company as much as $1 billion.