Facebook activated its Safety Check app to help people stay in touch and let friends and family know they’re safe following the deadly attacks in Belgium yesterday (March 22).  At least 34 people were murdered and scores of others wounded in back-to-back bombings of the Brussels airport and subway.

The current version of the social network tool, that was also used in November’s terrorist attacks in Paris, was developed at the Tel Aviv headquarters of Facebook Israel.

Some 4.1 million people used the Safety Check app in Paris. The app was also used in Nepal after a deadly earthquake in April 2015.

In 2011, Facebook Japan introduced the prototype of Safety Check, called Disaster Message Board, after the Japan earthquake and tsunami in March of that year. The technology was then sent for full development to the Israeli R&D team.

“Facebook has become like a public square, used by over a billion people, so being able to leverage the platform to enable people to receive reassurance that their loved ones are safe is something we are very proud to be a part of,” Facebook Israel’s Director of Engineering Roi Tiger said at a press conference following the Paris attacks.

The internet and social media are proving central to communication in the wake of the Belgium attacks. The Belgian government turned to Twitter to update the public about transportation and street closures. And a Belgian phone and Internet service provider opened its WiFi access point for free use immediately after the explosions.