AT&T has reached out to DSLReports.com to confirm that the ad injection technology being used at the Dulles airport was part of a limited trial that appears to have ended -- just as people started to realize it existed. As we noted yesterday, a computer scientist visiting Dulles Airport in DC noticed that AT&T's hotspot there was using technology by a startup named RaGaPa to overlay AT&T's ads over a user's browser stream. This was done by making three modifications to each page loaded and delivered by the hotspot.

"Our industry is constantly looking to strike a balance between the experience and economics of free Wi-Fi," AT&T said of its ad-injection experiment.

"We trialed an advertising program for a limited time in two airports (Dulles and Reagan National) and the trial has ended. The trial was part of an ongoing effort to explore alternate ways to deliver a free Wi-Fi service that is safe, secure and fast."

The problem with that statement is that by its very nature, ad injection technology is an attack on a user's existing, secure data stream. It's also not entirely clear if manipulating user data streams and third party content is entirely legal, which is why most ISPs caught engaging in this behavior are pretty quick to back away from the practice.