A man looks at Sony Corp's products at an electronics store in Tokyo May 26, 2011.[Photo/Agencies]

BOSTON/NEW YORK -- Hackers have again broken into Sony Corp's computer networks, this time claiming to have stolen customer data to show that the company's systems remain vulnerable to attack.

That marked the latest setback for Sony, which discovered in April that hackers had stolen data from more than 100 million of its accounts. Nobody has claimed responsibility for that attack.

The group LulzSec said on Thursday it broke into servers that run Sony Pictures Entertainment websites, and accessed the personal information of more than 1 million Sony customers.

To underscore the point that the Japanese electronics giant is unable to keep intruders out of its network, LulzSec published the names, birthdates, addresses, emails, phone numbers and passwords of thousands of people who had entered contests promoted by Sony.

A Sony spokesman said the company was "looking into these claims" but declined to elaborate.

"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?"

Reuters confirmed the authenticity of the data published about several of the sweepstakes entrants.

The attacks came on a day Sony executives were hauled before a Congressional committee to testify on the April attack of its gaming networks. Representatives criticized Sony for waiting several days to notify customers of the breach.

The US Federal Trade Commission could choose to review circumstances leading to this latest attack if Sony Pictures Entertainment failed to use proper procedures for protecting the data of its customers.

John Bumgarner, chief technology officer for the US Cyber Consequences Unit, a nonprofit group that monitors Web threats, was not surprised Sony's systems had again been breached.

"The system was unsecure," said Bumgarner, who last month warned of a string of security vulnerabilities across Sony's networks that he identified without special access to the electronics giant's computer systems.

He said he found vulnerabilities in the Sony Pictures Entertainment network as recently as last weekend.

The first hacking attacks in April, considered the biggest in Internet history, prompted Sony to shut down its PlayStation Network and other services for close to a month.

LulzSec has claimed responsibility for several hacks over the past month. It said it defaced the US PBS television network's websites, and posted data stolen from its servers on Monday to protest a "Front Line" documentary about WikiLeaks.

It has also broken into a Fox.com website and published data about contestants for the upcoming Fox TV talent show, "X Factor."

LulzSec also said on Thursday it had hacked into Sony BMG Music Entertainment Netherlands and Belgium. It previously disclosed an attack on Sony Music Japan.