Tor Project

The Tor Project's leave-no-traces browser now is available for Android phones.

The Tor Browser relies on a network of servers that send network requests over multiple intermediate links to hide who you really are when you visit a website. That can be useful if you don't want to be tracked -- whether you're an activist trying to avoid government monitoring or just an ordinary person trying to stay out of the clutches of ad companies.

"Mobile browsing is increasing around the world, and in some parts, it is commonly the only way people access the internet," Tor said in a blog post Tuesday. "In these same areas, there is often heavy surveillance and censorship online, so we made it a priority to reach these users."

The software is based on Mozilla's Firefox browser, an open-source project anyone can modify. Mozilla and Tor developers have been working more closely together on their two projects in recent years.

Ordinary browsers' private or incognito modes erase records of what websites you visited from your phone or laptop. Tor's approach eliminates records from websites, too. However, using it can cause inconveniences like tests to prove you're not a bot or websites showing up in the wrong language.

There's no version of the Tor Browser for iOS "due to restrictions by Apple," Tor said in its announcement. Tor steers iPhone and iPad owners toward a separate app, though, called Onion Browser.

For iOS, "several challenges prevent the interoperability that Tor developers are accustomed to on other platforms," the Tor Project said in a statement. Among them: a prohibition on a needed ability to generate new computing processes and a requirement to use only Apple's browser engine.

Apple didn't respond to a request for comment.

Originally published May 21, 12:50 p.m. PT.

Update, 1:35 p.m.: Adds mention of an alternative for iOS users. Update, 3:31 p.m. PT: Adds further comment from Tor about iOS difficulties.