Facebook has announced that they will be notifying their users if their account is being spied upon.
This development has come about because of suspicions by the website that a malicious attacker working for a nation-state has been targeting Facebook users.
Alex Stamos, the Chief Security Officer at Facebook, explained the move,
While we have always taken steps to secure accounts that we believe to have been compromised, we decided to show this additional warning if we have a strong suspicion that an attack could be government-sponsored.
We do this because these types of attacks tend to be more advanced and dangerous than others, and we strongly encourage affected people to take the actions necessary to secure all of their online accounts.
An example of this notification can be seen below.
Click here to read the full announcement.