Online advertising has ballooned into a roughly $45 billion-a-year business, to the benefit of Google, Yahoo, ad networks, and innumerable speciality and hobbyist Web sites.

One corner of this ecosystem that hasn’t managed to cash in on advertising is, by some measurements, the largest: broadband providers. So it may have been inevitable that they would seek additional revenue by monitoring their customers’ online activities and creating behavioral profiles that could yield hyper-relevant ads.