When Verizon mobile customers visit any website, the telecom company inserts a unique code into the headers of their Web traffic in order to track their behavior and interests across the Internet. Of course, this is for the benefit of advertisers. And it’s almost impossible to opt-out of the tracking.

So-called “perma-cookies” give advertisers a solution to the problem of the largely cookie-free mobile Web—the data that’s tracked when people browse websites. Verizon calls the anonymous number used by advertisers to identify you a Unique Identifier Header or UIDH.

As Ars Technica describes it:

The service allows websites to request advertisements along with the UIDH from a participating on-demand advertising network. The network can then request market-segment and geolocation information from Verizon to deliver the most appropriate advertisement.

Verizon’s partnerships for ad-tracking technologies were first revealed in May, but largely stayed under the radar until Electronic Frontier Foundation technologist Jacob Hoffman-Andrews tweeted about them last week.

“This is even at a more serious level than throttling traffic because ISPs are going in and modifying traffic in transit and that’s something that they should not be doing,” Hoffman-Andrews told Ars Technica. “They are paid by their customers to be trusted conduit for data, and they should be sending that data through faithfully rather than trying to insert or remove things.”

Opting out of the tracking is difficult, if not impossible. Verizon customers can opt-out of the Relevant Mobile Advertising program, but all that means is that Verizon won’t use the ID number to create targeted ads. But the tracking code in all your webpage requests (and those made by many of your apps) doesn’t go away. Advertisers can still use those anonymous digits to create a profile of your mobile activity.

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The only way to block the tracking code completely is to not use cellular data, instead relying on WiFi or a personal VPN.

Ad companies are already using UIDH numbers to target users. Kim Glaser, product manager at Run, said in an interview with AdExchanger that tracking users with a carrier identification provides more comprehensive data.

What we’re excited about is the carrier level ID, a higher-level recognition point that lets us track with certainty when a user, who is connected to a given carrier, moves from an app to a mobile Web landing page through an ad request and when they ultimately convert. We have access to an anonymous ID that allows us to track without any statistical model the ROI and the direct response that is occurring as a result of mobile investment.

Companies including Brightroll, BlueKai, Turn and Twitter’s MoPub ad exchange service use the carrier IDs as well. 

Lead photo by Sage_Solar