Personal details belonging to as many as 4.5 million job seekers have been stolen after hackers targeted recruitment site

Monster revealed that names, passwords, telephone numbers, email addresses and birth dates were among the information stolen, but it declined to reveal just how many users were affected. It is urging site users to change their passwords immediately.

"We regret any inconvenience this may cause you, but feel it is important that you take these preventative measures," Monster said in a message on its website. Security analysts claim that these details could be used by cyber criminals to open bank accounts and credit cards.

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"It's a horrendous breach," said Graham Cluley, of IT security company Sophos. "The information they have can be used to cause all kinds of mischief."

Sophos claims that four out of ten people use the same password to access multiple websites, which means the criminals behind the data theft could well gain access to banking and email accounts.

The Information Commissioner's Office is thought to be investigating the security breach.

This isn't the first time personal data has been stolen from the website. In August 2007, a virus attacked the website's database, stealing data belonging to more than 1.6 million job hunters.

See also: Facebook hackers increase attacks