Facebook users have been warned over a reported cyber attack which has put five million accounts at risk.

Nick Ascoli of PIXM, an anti-phishing browser extension, has issued the warning after millions of accounts were reportedly "stolen and breached".

The attack warning relates to a scam which sees mock Facebook pages sent out via Messenger in an effort to dupe unsuspecting victims into sharing their personal details.

Nick Ascoli warned: "Once the adversary has compromised the account of a Facebook user, they log in to that account – presumably automatically and then distribute new phishing links to all of that user's friends."

Head of the City of London Police’s National Fraud Intelligence Bureau, Superintendent Sanjay Andersen, said: “Criminals hack people’s email and social media accounts to access a wealth of valuable personal information about the individual, which they can use to commit fraud.

“This includes passwords for other accounts like online banking. Criminals also use compromised accounts to imitate the victim online and trick their family and friends into sending money.

“One of the most important things that you can do to improve the security of your online accounts is having two-factor authentication enabled. Not only will it prevent hackers accessing your accounts even if they have your password, but it will also keep your valuable information out of the hands of criminals.”