Facebook has accidentally revealed personal information about its members.

The social networking site divulged the dates of birth of many of its 80 million active users, even those who had requested that the information remained confidential.

Graham Cluley, senior technology consultant at Sophos, explained that the information was exposed during a public beta test of Facebook's new design.

"I was shocked to see people's full date of birth revealed, even though I knew they had their privacy set up correctly to supposedly hide the information, " he said.

"It is essential that users of social networks should have confidence that their privacy will be protected, and it is especially important with information like your date of birth which can be a golden nugget for a committed identity thief."

Cluley added that he informed Facebook as soon as he discovered the flaw, which now appears to have been fixed.

Sophos has published a video on its YouTube channel demonstrating the security hole.