The company said the practical impact of the bug will be minimal.
Facebook has fixed a privacy bug, which is believed to have exposed phone numbers and email addresses of 6 million users to others.
Facebook said: "We currently have no evidence that this bug has been exploited maliciously and we have not received complaints from users or seen anomalous behavior on the tool or site to suggest wrongdoing."
The company said the practical impact of the bug will be minimal and said it will work hard to make sure nothing like this will happen in the future.
Out of the total six million users, about 200,000 of the affected are reported to be the UK users.
The company said: "Even with a strong team, no company can ensure 100% prevention of bugs and in rare cases we don’t discover a problem until it has already affected a person’s account."
In 2011, a bug was exposed in Facebook, which allowed private photos of CEO Mark Zuckerberg to be downloaded.
Facebook recently said it received between 9,000 and 10,000 requests for data from the US government in the second half of 2012, which covers 18,000-19,000 of its 1.1 billion user accounts globally.