i can see how it could have been an accident that the cookie for the ad got added, but you have to be naive to think google didnt figure it out at some point, but did noting to stop it.
but at the same time i really have to ask who cares, its not a virus and just sees that you looked at a website... oh god they know what you looked at and put ads to go along with what you look at.
if a person was doing the looking i would have a problem, but its a machine.