While the feature allowed people in Paris to let their friends know they were safe after last week's attacks, Facebook received some criticism for having not activated the service after other terrorist attacks around the world. Until last week, Facebook had only used safety check following natural disasters.

"After the Paris attacks last week, we made the decision to use Safety Check for more tragic events like this going forward," Facebook CEO Mark Zuckerberg wrote on his page. "We're now working quickly to develop criteria for the new policy and determine when and how this service can be most useful."

Safety check provided plenty of worried friends and family members with peace of mind, but Facebook's selective use of the service was criticized by some who pointed out Facebook did not activate the service when -- one day before the Paris attacks -- twin bombings in a southern Beirut suburb in Lebanon left at least 43 dead and many more wounded.

"Until yesterday [the day of the Paris attacks], our policy was only to activate Safety Check for natural disasters," Zuckerberg wrote on his Facebook wall. "We just changed this and now plan to activate Safety Check for more human disasters going forward as well."

"We care about all people equally, and we will work hard to help people suffering in as many of these situations as we can," he said.