Facebook denied that there had been a privacy breach, saying the messages were old public messages, but admitted old messages had been reappearing.

Facebook’s director of engineering, Andrew Bosworth said the way people use Facebook has changed.

“In case there was any concern, these are just wall posts and not personal messages… people just forget how we used to use the wall,” he said.

Mark Zuckerberg, Facebook’s founder and chief executive, was also hit by the bug. His profile showed a message to a friend that said “2009 is going to be a huge year”.

A Facebook spokesman said: “A small number of users raised concerns after what they mistakenly believed to be private messages appeared on their Timeline.

“Our engineers investigated these reports and found that the messages were older wall posts that had always been visible on the users’ profile pages. Facebook is satisfied that there has been no breach of user privacy.”