In a note posted to the official Facebook Security page, the company says it will begin informing users if their account "has been targeted or compromised by an attacker suspected of working on behalf of a nation-state."
"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," Facebook's chief security officer, Alex Stamos, wrote. "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."
The company would not specify how it could determine whether an attack came from government-sponsored hackers, but said it would issue the warning "only in situations where the evidence strongly supports our conclusion." The warning asks users to turn on login approvals and recommends they "also take steps to secure" accounts on other services.