Hackers have broken into Sony Corp's computer networks and accessed the information of more than 1m customers to show the vulnerability of the electronic giant's systems in the latest of several security breaches undermining confidence in the company.

LulzSec, a group that claims attacks on US PBS television and Fox.com, said it broke into servers that run Sony Pictures Entertainment websites.

It published the names, birth dates, addresses, emails, phone numbers and passwords of thousands of people who had entered contests promoted by Sony.

‘From a single injection, we accessed EVERYTHING,’ the hacking group said in a statement.

‘Why do you put such faith in a company that allows itself to become open to these simple attacks?’

The security breach is the latest attack against high-profile firms, including defence contractor Lockheed Martin and Google Inc.

LulzSec's claims came as Sony executives were trying to reassure US lawmakers at a hearing on data security in Washington about their efforts to safeguard the company's computer networks, which suffered the biggest security breach in history in April.

Sony has been under fire since hackers accessed personal information on 77 million PlayStation Network and Qriocity accounts, 90% of which are users in North America or Europe.

Sony said at the time that credit card information may have been stolen, sparking lawsuits and casting a shadow over its plans to combine content and hardware products via online services.

Nobody has claimed responsibility for the April attack.

Sony said it was investigating the breach claimed by LulzSec and declined to elaborate. Sony shares in Tokyo fell 0.3%, in line with the broader market.