Facebook has confirmed findings of a CA security researcher that the social-networking site's Beacon ad service is more intrusive and stealthy than previously acknowledged, an admission that contradicts statements made previously by Facebook executives and representatives.

Facebook's controversial Beacon ad system tracks users' off-Facebook activities even if those users are logged off from the social-networking site and have previously declined having their activities on specific external sites broadcast to their Facebook friends, a company spokesman said via e-mail over the weekend.

Although according to the spokesman Facebook does nothing with the data transmitted back to its servers in these cases and deletes it, the admission will probably fan the flames of the controversy engulfing Beacon, which has been criticized by privacy advocates.

The Facebook spokesman did not initially reply to a request for further explanation on how the Beacon action gets triggered if a user is logged off from Facebook, when the social-networking site's ability to track its users' activities should be inactive.

It's also unclear whether Facebook plans to modify Beacon so it doesn't track and report on the off-Facebook activities of logged-off users.

Beacon is a major part of the Facebook Ads platform that Facebook introduced with much fanfare several weeks ago. Beacon tracks certain activities of Facebook users on more than 40 participating Web sites, including those of Blockbuster and Fandango, and reports those activities to the users' set of Facebook friends, unless told not to do so.

Off-Facebook activities that can be broadcast to one's Facebook friends include purchasing a product, signing up for a service and including an item on a wish list.

The program has been blasted by groups such as MoveOn.org and by individual users who have unwittingly broadcast information about recent purchases and other Web activities to their Facebook friends. This has led to some embarrassing situations, such as blowing the surprise of holiday presents.

On Thursday night, Facebook tweaked Beacon to make its workings more explicit to Facebook users and to make it easier to nix broadcast messages and opt out of having activities tracked on specific Web sites. Facebook didn't go all the way to providing a general opt-out option for the entire Beacon program, as some had hoped.

Then on Friday, just hours after Facebook had scored some points with its modifications to Beacon, Stefan Berteau, senior research engineer at CA's Threat Research Group, wrote in a note about Beacon's until-then unknown ability to monitor logged-off users' activities and send the data back to Facebook.

Users aren't informed that data on their activities at these sites is flowing back to Facebook, nor given the option to block that information from being transmitted, according to Berteau.

If users have ever checked the option for Facebook to "remember me" -- which saves users from having to log on to the site upon every return to it -- Facebook can tie their activities on third-party Beacon sites directly to them, even if they're logged off and have opted out of the broadcast. If they have never chosen this option, the information still flows back to Facebook, although without it being tied to their Facebook ID, according to Berteau.

Facebook's admission over the weekend contradicts previous statements from the company regarding this issue. For example, in e-mail correspondence with Facebook's privacy department, Berteau was told, among other things, that "as long as you are logged out of Facebook, no actions you have taken on other websites can be sent to Facebook."

A similar statement was made by a high-ranking Facebook official in an interview with The New York Times published Thursday.

"If I buy tickets on Fandango, and decline to publish the purchase to my friends on Facebook, does Facebook still receive the information about my purchase?," a Times reporter asked Chamath Palihapitiya, Facebook's vice president of product marketing and operations at Facebook

"Absolutely not. One of the things we are still trying to do is dispel a lot of misinformation that is being propagated unnecessarily," Palihapitiya replied.