The social network was deluged with complaints from members who claimed their old private messages have been re-published publicly on the social network.
Facebook admitted old messages were reappearing on profiles but quickly denied that there had been a privacy breach, as the messages were old public messages.
It appeared that members were shown old public "wall" postings that they wrongly believed were private messages. Observers said the outcry showed how the way people use Facebook has changed, as they have become more aware of their privacy online.
Facebook’s director of engineering, Andrew Bosworth, aimed to calm the panic.
Some users had claimed that messages they had sent privately on the social network between 2007 and 2009 were being republished into their public timelines on the site. Though it was not clear how many people were affected, there were complaints from users in Britain, America and in Europe.
Mark Zuckerberg, Facebook's founder and chief executive, was hit by the bug. His profile showed a message to a friend that said "2009 is going to be a huge year".