The NebuAd system places tracking cookies and sells users' Internet data to advertisers for targeting ads. Charter had been testing the system that privacy watchdogs Free Press and Public Knowledge called a "classic man-in-the-middle attack."

While NebuAd has worked with small Internet service providers, Charter is the country's fourth-largest ISP as well as a cable-TV and phone-services provider. That attracted the attention of Reps. Ed Markey (D-Mass.) and Joe Barton (R-Texas) of the House Committee on Energy and Commerce, who sent Charter a second letter expressing concerns and asking it to wait while Congress looks at the technology. The congressmen had also asked Charter to desist when it announced plans for the testing in May.

Markey, chairman of the House Subcommittee on Telecommunications and the Internet, said he was "pleased to hear that the company has decided to delay implementation of this program, which electronically profiled individual consumer Web usage." He added, "I urge other broadband companies considering similar user-profiling programs to similarly hold off on implementation while these important privacy concerns can be addressed."

That warning could effectively hamper plans by NebuAd and United Kingdom-based Phorm to expand their tracking technologies in the U.S. So far, their attempts have not progressed beyond testing.

Charter began testing tracking this month in Ft. Worth, Texas; San Luis Obispo, Calif.; Oxford, Mass.; and Newtown, Conn. Charter Senior Vice President Joe Stackhouse had assured high-speed Internet subscribers that targeted ads "will better reflect the interests you express through your Web-surfing activity. You will not see more ads -- just ads that are more relevant to you."