What is BFF message on Facebook?

It is a viral message that is getting surfaced on Facebook asking users to type 'BFF' in the comment section to check if their account has been hacked.

This is actually a hoax and a majority of people getting duped. This hoax came after the news broke out that data company CambridgeAnalyticagained access to millions of Facebook users' data and allegedly used it to try to influence the 2016 US presidential race in favor of Donald Trump.

As per the message, if the term 'BFF' turned green, the account is safe, but if it remained black, the account was hacked. Some comments turned green due to a new Facebook update.

A BFF message is a private message sent on Facebook by friends to each other. They use these messages to show their feelings towards each other and to express emotions such as happiness, sadness, confusion and love. The term comes from their initials: Best Friends Forever.
The meanings of the messages vary depending on who sends them; they can be as simple as “I miss you” or they can say more like “you are my life!”
The best way to keep your friends happy is by showing them your appreciation through these messages, especially if you want them to reciprocate for you. It helps establish genuine relationships that will last for a long time and become a part of your normal conversations.

The letters BFF means "Closest Friends Forever", and composing in the remark shows two hands "high fiving"[But not all the time]. This liveliness will be activated by bff or bffs. Bff implies Best companions until the end of time