The FBI has published a warning about a scam targeting people on Facebook Messenger.
The messages contain a link which could steal a user's login credentials by taking them to another website which appears to be the Facebook login page, when in fact it is controlled by a fraudster.
Other forms of the scam could redirect users to a page that automatically harvests their login credentials.
In a personal example of how the scammers work, an FBI staff member said they were contacted by a friend on Facebook Messenger.
They explained: "The message included a video link and read: 'Hey I saw this video. Isn't this you?'
"I was suspicious, so I didn't click on the link.
"The next day he contacted me outside of the app and said that fraudsters had hacked his account and to not click on any of the links that were sent because they contained a computer virus."
Warning the public, the FBI said: "The best way to spot and avoid these scams is to avoid clicking on any links that you receive from friends or family until you contact the sender outside of app to verify that he was the one who really sent the message.
"If you are concerned about the legitimacy of a particular account, report it through Facebook."
Sky News has contacted Facebook for comment.