A Congressional inquiry into ad targeting has prompted Yahoo to expand its privacy controls, allowing users to decline ads served to them based on their browsing habits.

The expanded provision, which will probably be available at the end of the month, enables users to opt out of behaviorally-targeted ads across Yahoo's entire portal rather than just those run on partner sites.

Behaviorally-targeted ads are sponsored messages directed at users based on their previous search, purchasing or other online activity. In June it was revealed that Google uses previous search activity to serve ads against current searches. To maintain a good rapport among users that demand transparency, the search giant added a small "More Details" link to search results, which tell users how their data is being used.

The link to Yahoo's Privacy Center will be on nearly every page of its network — a "one-up" on Google, which made much ado about the tiny privacy link it added to its homepage in July. Yahoo will also advocate its new policy through a PSA campaign about customized advertising.

This doesn't mean Yahoo will stop collecting and retaining user data, which it says is necessary for fraud detection and law-enforcement requests. And other types of ad-serving, based on data like search terms or location, will not be affected, writes the Associated Press.

The Congressional inquiry on ad targeting was sent to 33 companies, including AOL, Microsoft, Google, and internet service providers Cablevision and Cox Communications. A similar hearing by a Senate subcommittee focused on behavioral targeting practices.

The government scrutiny is making internet marketing companies — which are accustomed to policing themselves — nervous. The FTC let them off the hook late last year when it said it would not adopt stricter policies, and small steps have been taken to make ad serving more transparent to users, but privacy advocates continue to lobby for more control.

Some say that, far from setting a user-friendly privacy precedent, Yahoo hopes to endear itself to Congress to avoid a clampdown on its search deal with Google.