91Èȱ¬

A notorious hacker group has warned the NHS that its computer networks are vulnerable to cyber attack.

Lulz Security, which claims to have been behind a recent hack on Sony, sent an email to NHS administrators revealing it had found a way to breach the service's network.

But the Department of Health was quick to deny that any patient information was at risk.

The hackers said they did not intend to steal any data.

Styling themselves as "pirate ninjas", LulzSec posted on Twitter the e-mail it sent to the NHS.

"While you aren't considered an enemy - your work is of course brilliant - we did stumble upon several of your admin passwords," the e-mail read.

It lists the stolen information - but blacks out the names in the tweet.

"We mean you no harm and only want to help you fix your tech issues," the mail continued.

The Department of Health played down the warning.

"This is a local issue affecting a very small number of website administrators. No patient information has been compromised," a Department of Health spokesperson told the 91Èȱ¬.

"No national NHS information systems have been affected. The Department has issued guidance to the local NHS about how to protect and secure all their information assets."

Like many hacker groups, LulzSec appears to be a loosely organised collective with no-one really in charge.

It claims to specialise in finding poorly protected websites to attack. Information they steal is sometimes posted to the web.

The group has made the headlines in recent months for a number of hacking attacks.

At the beginning of June it claimed to have broken into servers that run SonyPictures.com and accessed the details of a million users.

A day later it claimed to have hacked Nintendo's website.