Facebook founder Mark Zuckerberg has allegedly been targeted by hackers, with a group claiming to have accessed several of the billionaire's social media accounts.
A hacking group called OurMine used its Twitter account to claim access had been gained to the entrepreneur's Twitter, Instagram, LinkedIn and Pinterest accounts on Sunday.
Messages were sent to Mr Zuckerberg and from his own account claiming to be from OurMine, who said they were "just testing your security".
In response to the messages, the Facebook founder denied his security had been compromised, telling the hackers to "go away". The series of tweets has since been deleted.
However, a screenshot of Mr Zuckerberg's Pinterest account was posted to Twitter by developer Ben Hall that appeared to show it had been renamed "Hacked by OurMine team".
Some reports have suggested that stolen password data from a cyber attack on LinkedIn in 2012 may have led to the hackers gaining access to Mr Zuckerberg's accounts, with some claiming that the social network boss may have used the same password across several sites - which could have caused the breach.
Many of the accounts in question are relatively inactive - Zuckerberg has not sent a tweet since 2012, while his Instagram account shows only 30 photos.
Facebook has not commented on the alleged breach, though it is understood that the company's security systems prevented Mr Zuckerberg's Instagram account from being fully accessed. Instagram is owned by the social media giant.
Richard Parris, head of cybersecurity company Intercede, said the incident should "concern us all", adding that the current system of a username and password combination was a "fundamentally flawed approach to internet security" and called for more innovation in the field.