Softbank Corp. said Friday it has confirmed that information on some 4.52 million users of its Yahoo! BB high-speed Internet service had been stolen from its data base.

The theft, which came to light earlier this week in two separate extortion cases targeting the company, is an unprecedented personal information leak in terms of volume.

As a gesture of apology, Softbank said it will send 500 yen gift certificates to all the victims -- including 2.1 million former subscribers and temporary free trial users -- and all other subscribers whose information was not leaked. The measure could cost about 4 billion yen, it said.

Softbank also said top executives will take pay cut as a gesture of responsibility, with chief executive Masayoshi Son's monthly salary cut by half for six months.

"As I look back, there was room for further improvement (in security)," Son told reporters in Tokyo. "We fully regret what happened, and apologize."

He said it was yet known how the data were stolen.

The company said that while the stolen data include user names, addresses, phone numbers and e-mail addresses, they do not include credit information such as credit card numbers or bank account numbers.

Four suspects were arrested Tuesday in the two separate extortion bids, in which the suspects allegedly tried to get Softbank to buy back the stolen client data.

The company had been working to confirm the authenticity of the data confiscated by authorities since Tuesday and completed it early Friday, Son said.

Son said the incident did not change the company's target to attract 6 million users by the end of September 2005.

Softbank's Yahoo! BB service, using asymmetric digital subscriber line, has been rapidly gaining users since its start in 2001.

It had 3.81 million users as of the end of January.