People's private Facebook messages are being sold on the internet for anyone to read.

Tens of thousands of people's secret chats are being traded without their knowledge, according to a BBC report.

In all, at least 81,000 people's messages are being swapped online, the report claimed. Many of them came from Ukraine and Russia, but many more besides were from users in the UK, the US, Brazil and elsewhere.

How to stop Facebook from revealing everything about you Show all 9 1 /9 How to stop Facebook from revealing everything about you How to stop Facebook from revealing everything about you Lock your profile down If you haven’t done this already, do it now. In Settings, hit the Privacy tab. From here, you can control who gets to see your future posts and friends list. Choose from Public, Friends, Only Me and Custom in the dropdown menu. How to stop Facebook from revealing everything about you Limit old posts Annoyingly, changing this has no effect on who’s able to see your past Facebook posts. Instead, on the Privacy page, you have to click on Limit Past Posts, then select Limit Old Posts and finally hit Confirm on the pop-up. How to stop Facebook from revealing everything about you Make yourself harder to find You can stop completely random people from adding you by selecting Friends of Friends from the dropdown menu in the Who can send you friend requests? section of the Privacy page. It’s also worth limiting who can find your Facebook profile with your number and email address. At the bottom of the page is the option to prevent search engines outside of Facebook from linking to your profile. How to stop Facebook from revealing everything about you Control access to your Timeline You can limit who gets to post things on your Timeline and who gets to see posts on your Timeline too. In Settings, go to Timeline and Tagging and edit the sections you want to lock down. How to stop Facebook from revealing everything about you Block people When you block someone, they won’t be able to see things you post on your Timeline, tag you, invite you to events or groups, start conversations with you or add you as a friend. To do it, go to Settings and Blocking. Annoyingly, you have to block people on Messenger separately. You can also add friends to your Restricted list here, which means they’ll still be friends with you but will only be able to see your public posts and things you share on a mutual friend's Timeline. How to stop Facebook from revealing everything about you Review tags One of Facebook’s handiest privacy features is the ability to review posts you’re tagged in before they appear on your Timeline. They’ll still be visible on the News Feed while they’re fresh, but won’t be tied to your profile forever. In Timeline and Tagging, enable Timeline review controls. How to stop Facebook from revealing everything about you Clean up your apps You can view a list of all of the apps you’ve connected to your Facebook account by going to Settings and Apps. The list might be longer than you expected it to be. It’s worth tidying this up to ensure things you no longer use lose access to your personal information. If you don’t want to log into websites and apps with your facebook account, scroll down and turn Platform off. How to stop Facebook from revealing everything about you Change your ad preferences You can view a list of everything Facebook thinks you’re into and tinker with your ad preferences by going to Settings and Adverts. A lot more information is displayed on the desktop site than the app, so we’d recommend doing this on a computer. How to stop Facebook from revealing everything about you Download your data Facebook lets you download all of the data it has on you, including the posts you’ve shared, your messages and photos, ads you’ve clicked on and even the IP addresses that are logged when you log in or out of the site. It’s a hell of a lot of information, which you should download to ensure you never over-share on the social network again.

Compromised accounts that were caught up in the hack are being sold for just $0.10 each, according to the report.

The leak does not appear to have come from Facebook itself, despite a series of data scandals. Instead, it appears to have been the consequence of malicious browser extensions, which install themselves onto people's computers and are then able to watch their activity and break into their account.

The hackers claimed to have access to 120 million accounts, but they appear to have been exaggeration the scale of the attack. However, the hackers showed some evidence of having the messages of some 81,000 people, a number of which were checked with account holders and confirmed to be genuine.

Facebook said it had contacted browser companies to ensure that the malicious extensions were no longer used. But it advised its users to check the extensions they have installed and remove any that might be malicious.

“Based on our investigation so far, we believe this information was obtained through malicious browser extensions installed off of Facebook,” Guy Rosen, Facebook's vice president of product management, said in a statement emailed to a number of outlets.

“We have contacted browser makers to ensure that known malicious extensions are no longer available to download in their stores and to share information that could help identify additional extensions that may be related,” Rosen said. “We have also contacted law enforcement and have worked with local authorities to remove the website that displayed information from Facebook accounts.”