Facebook founder, Mark Zuckerberg apologized to users on Wednesday for their controversial web-based advertising system, Beacon, which publishes information about members' off-site purchases to users' friends.

Zuckerberg publicly apologized via the company blog after weeks of criticism since the launch of the ad system on November 7. The advertising model uses social advertising technology which tracks a user's web purchases. Zuckerberg's aim was to convert private commerce into public endorsements. Controversy arose because some users complained that they were not given the opportunity to decide whether to participate.

We missed the right balance. At first we tried to make it very lightweight so people wouldn't have to touch it for it to work. We've made a lot of mistakes building this feature, but we've made even more with how we've handled them, Mark Zuckerberg said.

We simply did a bad job with this release, and I apologize for it. I'm not proud of the way we've handled this situation and I know we can do better.

How does it work?

Websites sign up to be a partner of Facebook's Beacon program. By doing so, they receive a code on their website which then sends feedback to Facebook of the users' activity on their website. For example, a Facebook registered user visits eBay.com and purchases a Heroes DVD set. That purchase data is sent back to Facebook. This allows advertisers to target the user with further Heroes products. Over 40 websites have signed up to Beacon, including The New York Times, Sony Online, TripAdvisor, Blockbuster, eBay and Amazon.

MoveOn.org, a non-profit liberal public policy advocacy group, said Beacon was an invasion of privacy for Facebook users and could cause embarrassment to its users by publicizing their online purchases. They went on to set up a Facebook group called Petition: Facebook, stop invading my privacy! which quickly grew to over 60,000 members in two weeks.

The self-declared privacy avengers group led Zuckerberg to apologize to the popular social-networking sites users. The Beacon feature is no longer automatically enabled. Instead, users must specifically activate it.

Last week we changed Beacon to be an opt-in system, and today we're releasing a privacy control to turn off Beacon completely. You can find it here. If you select that you don't want to share some Beacon actions or if you turn off Beacon, then Facebook won't store those actions even when partners send them to Facebook, concluded Zuckerberg.