Earlier this year, AT&T's Cingular division and Travelocity both pledged not to advertise anymore via adware--programs that slip onto PCs and inject ads into a user's browser. Verizon took a stance against computer invaders when it became a sponsor of an antispyware initiative. Yet, in March, ads from all three companies were being distributed through adware.

hese businesses, along with Comcast and Vonage, acknowledge that their ads have surfaced in adware, but say they never intended for that to happen. The incidents raise a troubling question: Have advertising networks grown so complicated that sponsoring firms can't control where their ads appear, or are the companies simply not being vigilant enough?

Cingular and Travelocity say they prohibit the use of adware by advertisers they hire. Travelocity says that as soon as it found out its ads were showing up in adware, it "immediately suspended and eventually terminated its advertising campaigns with partners who may have been associated with those violations." Cingular says that it took similar action.

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