The chief executive of Facebook has issued a personal apology for introducing a new advertising feature that was widely criticised for invading users' privacy.

Mark Zuckerberg said that the social networking website had made "a lot of mistakes" building the feature, and that users would now have to give their consent before their actions elsewhere on the web were tracked and broadcast to friends on the site.

In a blog post on Facebook, Mr Zuckerberg said: "I'm not proud of the way we've handled this situation and I know we can do better. We simply did a bad job with this release, and I apologise for it."

The feature, called Beacon, was unveiled last month, and was designed to allow companies to attach advertisements to messages that would be sent to a user's friends when, for instance, the user made purchases from other sites.

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Several large firms, including Coca-Cola, Blockbuster, Sony and Microsoft had signed on as "partners" in the programme, which Facebook was hoping would boost its revenues using viral, "word of mouth" style advertising.

But it soon emerged that the feature was what is known as "opt-out", meaning that a Facebook user's purchases and activities on such sites would be relayed to their friends unless the user explicitly requested that the feature be switched off.

Users began posting angry messages on Facebook.com saying that details of Christmas gifts that were meant to be surprises had been made public, and that the boxes which gave them the opportunity to opt out of the feature were too small.

Advertising executives also expressed surprise that the onus was on users to turn off the feature.

Soon after the release, MoveOn.org, the US campaign group, began a petition – eventually signed by more than 50,000 people – which lobbied Facebook to change the way the feature worked, saying it had violated users' privacy and sullied the reputation of social networking sites.

Facebook, which is under pressure to turn its vast subscriber base into revenues, initially refused to allow a "universal opt-out" for Beacon, and said that MoveOn had "misrepresented" the way the service worked.

But last week the site admitted that Beacon could be "kind of confusing", and apologised if the feature had spoiled users' holiday gift-giving plans.

In yesterday's blog post, Mr Zuckerberg told the site's 85 million users: "We've made a lot of mistakes building this feature, but we've made even more with how we've handled them. It took us too long after people started contacting us to change the product so that users had to explicitly approve what they wanted to share."

Rob Norman, chief executive of GroupM Interaction, the media buying arm of WPP, said: "The success of the internet advertising model is based on people being targeted in a non-personally identifiable way, using their behaviour. The problem with Beacon (as it was) was that it made people's personally identifiable information public on an involuntary basis. Facebook absolutely had to change that."

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