The number of people accessing Facebook via the ”dark web” now stands at 1 million per month, the tech giant announced today (April 22). Facebook has maintained an “Onion” site that resides on the Tor network, which forms part of the so-called dark web, for about a year and a half. This is the first time the company has revealed details about its presence in this shadowy corner of the internet.

Tor preserves users’ privacy by disguising their identity and location by bouncing web traffic randomly through a far-flung network of servers. (Tor is short for The Onion Router, since it adds layers of anonymity to traffic that are tricky to peel away.) The Tor code is open-source and its servers are operated by volunteers.

The number of people connecting to Facebook over Tor is growing at a steady clip. Facebook said that in June last year some 525,000 people accessed its dark-web site. Traffic has grown in a “roughly linear” pattern sine then, according to Facebook, meaning about 50,000 new users are have been accessing the social network via Tor each month.

“People who choose to communicate over Tor do so for a variety of reasons related to privacy, security and safety,” wrote Alec Muffett, a Facebook engineer in London who leads the company’s work on its dark-web presence. “It’s important to us to provide methods for people to use our services securely—particularly if they lack reliable methods to do so.”

Indeed, Facebook has added more ways to access the site on the dark web over time. In January, it made its Onion site accessible to smartphones running the Android operating system.

Traffic to the Tor network often spikes in places when governments try to restrict access to social networks. This was the case in Bangladesh at the end of 2015, when the government cut off access to Facebook for around three weeks, citing security concerns following controversial death sentences handed down by the courts. Traffic to the Tor network originating in Bangladesh surged during that period, although Facebook hasn’t clarified whether it saw a similar uptick in traffic to its own dark-web site.

“To be clear, temporary increases have more to do with current events than access restrictions,” said Melanie Ensign, a Facebook spokesperson.