In recent weeks, Verizon and AT&T have been caught up in a privacy firestorm over their use of so-called “permacookies,” a method of tracking what their users do while browsing the Web with the intent of sharing that data with advertisers. Verizon’s permacookie program lives on, but AT&T has ceased the practice, ProPublica reported on Friday.

At least for now.

AT&T tells ProPublica that its use of permacookies was “part of a test,” which has since wrapped up, but the company says that it “may still launch a program to sell data collected by its tracking number.” For its part, AT&T says that it will allow customers to opt out of the program if—or when—it decides to use permacookies for advertising purposes.

The story behind the story: Permacookies aren’t cookies in the traditional sense: Instead, they’re unique identifiers appended to website addresses you type in on your device that let carriers see what kinds of sites you visit.

Permacookies exist for the same reason traditional tracking cookies exist—so advertisers can see what sorts of things you might be interested and serve up related ads in the hopes that you’ll click on them. But unlike regular tracking cookies, which you can easily delete from your browser or block entirely, there’s no way of removing or blocking permacookies since they’re handled entirely by the carrier.

Permacookies here to stay?

Despite the outcry from consumers and activists, it’s hard to shake the feeling that permacookies aren’t going away now that the proverbial cat is out of the bag. Both Verizon and AT&T have said they allow (or will allow) customers to opt out of the advertiser data sharing program, as ProPublica notes (though Verizon won’t let you opt out of the identifier program), but you’re still very much at the mercy of the carriers.

If you’re on Verizon and are concerned about the privacy implications, our Ian Paul has a couple suggestions: First, use Wi-Fi instead of the cellular network whenever possible so you bypass Verizon’s network entirely. If that’s not practical, though, consider using a VPN to help keep your Web browsing private.