Claims that the privacy of direct messages sent between Facebook users had been compromised and that the messages were appearing publicly on users' timelines are false, the social networking service has said.

There was confusion on Monday amid reports in France that non-public messages sent in the years from 2007 onwards had started to appear in timelines, sparking many users to check back in the fear that potentially embarrassing private messages had become widely viewable.

Facebook's share price fell 9.1% to $20.79 at the close in New York on the back of the fears, the biggest drop since 27 July. The stock has slumped 45% since its May initial public offering, and hasn't traded above its $38 IPO price since the day after the share sale.

A Facebook spokesperson later said that an investigation was launched after "a small number" of users raised concerns after what they believed to be private messages appeared on their timelines.

"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," he added.

The company has suggested that much of confusion was because of how differently people used Facebook in 2007, when there was no comments feature and the like button did not exist. As a result, wall posts were used more often and in some cases people may have used wall posts instead of private messages by mistake, according to the company.

Facebook investigated a similar claim late last year, which the company found to be false.

It also said on Monday that, from a technical perspective, private messages and wall posts were treated very differently and that no mechanism has ever been created that would allow a private message to be published on timelines.

One suggestion for why the issue emerged on Monday was because France, where the first cases of people expressing concern about the potential exposure of private messages, was the most recent place where Facebook's Timeline feature was being introduced.