AT&T has stopped stamping unique ID numbers on its customers, which allowed websites and ad networks to track them across the web. The telco promised to offer an opt-out switch if the system returns.
"We have completed testing of the numeric code that would be part of any new mobile Relevant Advertising program we may launch," AT&T said in a statement to The Register today.
"Any new program we would offer would maintain our fundamental commitment to customer privacy. Customers will be able to opt out of the ad program, and not have the numeric code inserted on their device. Customer trust is important to us, and customers have choices about how we use their information."
Some mobile network providers are getting a little sick of customers binning standard web cookies that track their movements online, depriving the poor telcos of much-needed advertising revenue and profile-building capabilities for targeted ads.
Verizon pioneered the use of "supercookies" – mandatory HTTP headers that can't be stripped out or blocked – two years ago, but privacy experts raised concerns over the scheme. Verizon's system has an opt-out capability, whereby the telco doesn't track the headers, but even if customers do say no, the headers are still added to every visit they make to a website, and can be tracked by third parties.
AT&T's system was broadly similar to Verizon's, giving the firm the ability to bypass pesky privacy tools. That said, AT&T's system was apparently harder for third-party advertisers to track, as a spokesman explained.
"We have been testing a numeric code that changes every 24 hours on mobile devices as an important protection against unauthorized tracking. It would be used to help serve ads on an anonymous basis," he said.
The move sees Verizon on its own in insisting on giving each customer a virtual tracking device on their handsets, and the telco is seeing an increasing amount of customer concern over the issue. The EFF has stepped up its efforts to get the system replaced with something more privacy friendly.
"This move by AT&T leaves Verizon out in the cold as the only remaining US provider to insert these tracking headers, and shows that concerned customers can produce meaningful change in their carriers' policies," said EFF staff technologist Jacob Hoffman-Andrews on Friday.
"It is also a victory for carrier non-interference with customer data. We call on Verizon to follow AT&T's lead and terminate their tracking header injection program or convert it to a true opt-in, immediately." ®