Last updated at 13:11 25 September 2007

Facebook is under investigation for failing to protect children from paedophiles on its site, it has been announced.

The hugely-popular but increasingly controversial social networking site has been subpoenaed by New York attorney general Andrew Cuomo after it failed to take action when undercover investigators were solicited for sex while posing as teenagers on the site.

Investigators who set up profiles as 12 to 14-year-olds found their decoys were quickly contacted by other users seeking sex, Mr Cuomo said.

He also claimed Facebook bosses did not respond to written complaints on several occasions.

"My office is concerned that Facebook's promise of a safe website is not consistent with its performance in policing its site and responding to complaints," MrCuomo said.

"Parents have a right to know what their children will encounter on a website that is aggressively marketed as safe."

No charges have been filed, but Facebook has been ordered to release documents relating to the security promised to its 42 million users and how it resolves complaints.

The attorney general's office is investigating whether Facebook's advertising and statements to users are "materially misleading" under state laws that prohibit deceptive business practices, Mr Cuomo said in a letter to Facebook's founder and chief executive, Mark Zuckerberg.

Facebook spokesman Brandee Barker said the concerns were being taken "very seriously".

"As our service continues to grow, so does our responsibility to our users to empower them with the tools necessary to communicate efficiently and safely," he said.

"We strive to uphold our high standards for privacy and are constantly working on processes and technologies that will further improve safety and user control on the site."

The investigation comes as the Wall Street Journal reports that Microsoft is in talks to buy a stake in Facebook in a deal that could value the networking site at more than £5billion.

The price would justify Mr Zuckerberg's decision to turn down Yahoo's $900 million (£447 million) offer in September last year to buy the whole company.

Microsoft is said to be willing to pay up to $500 million (£248million) for a five per cent stake. The move could spark a bidding war with Google.

Facebook launched in February 2004 and membership was initially restricted to Harvard students before being extended to other Ivy League universities.

Since September last year it has been made available to the general public.