Sony Corp. Chief Executive Howard Stringer apologized for a massive data breach of the company's online game networks—the first public remarks by the top executive as Sony works to reassure its customers following the theft of personal data from more than 100 million online accounts.

"I know this has been a frustrating time for all of you," Mr. Stringer said in a blog post addressed to Sony customers late Thursday evening. "Let me assure you that the resources of this company have been focused on investigating the entire nature and impact of the cyber-attack we've all experienced and on fixing it."

The intrusion, which occurred last month, resulted in the theft of names, email addresses and possibly credit-card information from its PlayStation Network and Sony Online Entertainment gaming services. Sony took down the PlayStation Network over two weeks ago to investigate the intrusion and secure the network from future attacks.

On Thursday, Sony also revealed details of a plan to provide its customers with free identity-theft prevention services for 12 months. Sony said the prevention service, provided through a company called Debix Inc., will alert Sony customers to unauthorized use of their personal information and a $1 million insurance policy if they become the victims of identity theft.