Mobile carriers around the world are tracking their users with an undetectable and unremovable kind of "supercookie."
Tracking headers, sometimes called "supercookies," are injected into your connection by internet companies at the network level so users have no control over their use. Tracking headers transmit information like your device ID and phone number to the site you're trying to access, and advertisers can use them to serve you targeted ads.
According to a new report by internet watchdog Access, which used data from Access' web test for tracking headers, roughly 15 percent of users represented in the nearly 180,000 tests that were run were being tracked.
The company tracking the most users was Verizon in the US, despite the company's opt-out program, followed closely by AT&T, which actually did stop using tracking headers last year. The report notes that the instances of AT&T customers being tracked dropped to zero after 17 weeks of people running the test, which launched in October of 2014.
Outside of the US, Vodafone in Spain and the Netherlands were big offenders. Telefonica in Spain, Bell Canada, and Viettel in Peru—a subsidiary of a Vietnamese internet company run by the military—also all made the list. Vodafone in the Netherlands had the highest percentage of tracked users: 75.6 percent.
Verizon is currently embroiled in legal action regarding tracking headers, and AT&T has stopped using the technology. Even so, the report concludes, it's highly unlikely that these companies would give up their tracking power.
They may already be using the next generation of tracking tech—we might just not know about it yet.