The personal details of millions of people have been stolen from one of the UK's largest recruitment websites in potentially the largest data theft ever in Britain.
Hackers accessed the confidential information provided by 4.5 million people registered with Monster.co.uk and now hold their user names, passwords, telephone numbers and email addresses. The company said other information including client birth dates, gender and ethnicity had also been taken, along with "basic demographic data".
Monster revealed in a statement on Friday that its database had been illegally accessed but the scale of the breach did not emerge until last night.
Fears were growing that hackers may have gained access to user bank accounts, since many people use the same password and email address to access multiple websites.
Friday's statement was signed by the company's senior vice president, Patrick Manzo, and said the information taken did not include resumes.
Customers were advised to change their passwords the next time they logged on to the site and were told their email addresses could be targeted by the hackers as they tried to retrieve further information.
If confirmed, the theft will rank as the largest data security breach since the Government lost the details of 25 million child-benefit recipients in 2007.
Monster refused to say exactly how much data had been accessed, but said the hackers had not been able to access its customers' financial details.
A spokeswoman said the company was taking "appropriate law enforcement action".