Popular social-networking site Facebook.com recently admitted to tracking offline users with its ad service.

According to a company spokesman, Facebook’s Beacon ad system tracks users’ off-Facebook activities, “even if those users are logged off…and have previously declined having their activities on specific external sites broadcast to their Facebook friends.”

This add system can “[track] certain activities of Facebook users on more than 40 participating websites, including those of Blockbuster and Fandango, and reports those activities to the users’ set of Facebook friends, unless told not to do so,” says pcworld.com.

Despite Facebook’s privacy contract which states that “as long as you are logged out of Facebook, no action you have taken on other websites can be sent to Facebook,” the opposite is true.

According to a Facebook spokesman, the site “does nothing with the data transmitted back to its servers in these cases and deletes it,” but, if that’s true, then one wonders why tracking would be necessary?

“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,” says Stefan Berteau, senior research engineer at CA’s Threat Research Group.

Since initial reports, Facebook founder Mark Zuckerberg has publicly apologized, and the site has been changed so users can shut off Beacon completely, going against previous reports that they would not offer users a “universal opt-out.” Maybe the fifty thousand Facebook users who signed an anti-Beacon petition helped sway the decision.

Obviously, internet security remains a current and relevant issue.

Nate Elliott of Jupiter Research agrees, saying, “The controversy shows that consumers want to be in control of how their information is to be used. These are people who are clearly comfortable about putting a lot of personal information online but they want to be in control of who they share this with. Facebook has taken too much of the control away from users.”

Warns Ed Mayo, Chief Executive of the UK’s National Consumer Council, “Parents should be aware that the internet is highly commercial. Every hour that a child spends in front of the computer is like letting them run loose in a shopping center.”

Elliot hopes “other social networks have been paying very clear attention to this and [are] learning some lessons.”