AT&T to scrap US phone web tracking codes AT&T Mobility, the United States' second-largest mobile phone provider, says it's no longer attaching hidden internet tracking codes to data transmitted from its users' smartphones. THE practice made it nearly impossible to shield its subscribers' identities online. The change by AT&T essentially removes a hidden string of letters and numbers that are passed along to websites that a consumer visits. It can be used to track subscribers across the internet, a lucrative data-mining opportunity for advertisers that could still reveal users' identities based on their browsing habits. Verizon Wireless, the country's largest mobile firm, said on Friday it still uses this type of tracking, known as "super cookies." Verizon spokeswoman Debra Lewis said business and government customers don't have the code inserted. The tracking codes are part of the latest plan by the mobile phone industry to keep tabs on users and their devices. While the codes don't explicitly contain personal information, they're unique and nonetheless sent to websites alongside personal details that a user may submit voluntarily - like a name or a phone number. AT&T said on Friday its tracker was part of a testing project that's been phased off of its network. "This is more like a licence plate for your brain," said Jacob Hoffman-Andrews, a senior staff technologist with the Electronic Frontier Foundation, a civil liberties organisation that opposed the practice. Everything you wonder about, and read, and ask the internet about gets this header attached to it. And there are ad agencies out there that try to associate that browsing history with anything that identifies you. The magazines Wired and Forbes first reported last month that Verizon and AT&T were inserting the tracking numbers, even if their subscribers wanted to opt out. The investigative website ProPublica also discovered that Twitter's advertising arm was using Verizon's tracking codes, which could be used to build a dossier about a person's behaviour on mobile devices.