The latest in a long line of privacy issues has hit Facebook users.
A bug allowed users to see their friends' private chats by using the feature that previews how a profile will look when viewed by others.
The vulnerability has now been fixed.
Facebook temporarily disabled chat while technicians addressed the flaw.
"Chat is unavailable as we work quickly to fix a bug reported to us," announced the company on their Facebook page.
"It should return to normal soon. Because of the bug, people could view friends' chat messages and friend requests for a limited amount of time if they manipulated the 'preview my profile' feature in a specific way. We've fixed that issue and took down Chat as soon as we became aware of it. We apologize for the inconvenience."
The mistake comes after a long line of controversial privacy blunders by the company, who recently made users' profile information available to third party websites, allowing for the personalisation of web content.