More Than a Million People Are Accessing Facebook in Secret by David Meyer @FortuneMagazine April 22, 2016, 7:17 AM EDT E-mail Tweet Facebook Linkedin Share icons People use the Tor anonymizing network to access all kinds of online services without revealing their identity—the shadier services grab the headlines, but there’s a lot of legitimate use too. Facebook fb , for example. The social network said Friday that over a million people accessed Facebook through the Tor network in the last 30 days, up from around 525,000 last June. The growth is roughly linear, wrote Facebook software engineer Alec Muffett. People may want to access Facebook through Tor in order to hide the fact they’re doing so from their oppressive governments, for example. The facility also makes it possible to get through to Facebook if a government has blocked it (say, in Iran or China). Get Data Sheet, Fortune’s technology newsletter. “People who choose to communicate over Tor do so for a variety of reasons related to privacy, security and safety…It’s important to us to provide methods for people to use our services securely—particularly if they lack reliable methods to do so,” Muffett wrote. Tor works by routing your Internet traffic through a series of encrypted layers to disguise its origin. The outfit uses the analogy of the layers in an onion—”Tor” stands for “The Onion Router.” The Tor browser, which bundles the technology with a variant of Firefox, allows people to access regular services anonymously, and also to access so-called hidden services that can’t be found through a regular browser. These use “.onion” address extensions. Back in 2014, Facebook started providing its own .onion address for the benefit of Tor users. This was partly to provide extra security to those users—it allows end-to-end encryption—and partly because Facebook’s regular service sometimes mistook people accessing it via Tor as possible attackers. For more on Facebook and anonymity, watch: So-called “botnets,” used for sending spam and launching denial-of-service attacks, also route traffic through various connections in a way that looks quite similar to Tor’s methods. So those who were legitimately trying to access Facebook through Tor previously found themselves having to complete all sorts of extra security checks to demonstrate that they were human. Since then, Facebook has also made it possible to use Tor’s anonymizing technology in conjunction with the Android Facebook app, and it helped to reserve the .onion domain extension for hidden services.