Facebook's recent advertising-related changes to the popular social networking site have not proved popular with many users.

The "Beacon" system, a controversial new advertising program that flags user's retail purchases in Facebook's news feeds has been the target of mass protest from consumer groups.

More than 50,000 people signed a petition on US site MoveOn.org demanding the site made changes to the Beacon feature.

Facebook has made the changes to the system, and now users have to opt-in in order for their purchase info to show up.

Facebook's UK PR team has issued a statement, and given info on Beacon in order to try and quell user unrest about the new features on the site.

"We appreciate feedback from all Facebook users and made some changes to Beacon in the past day. Users now have more control over the stories that get published to their Mini-Feed and potentially to their friends' News Feeds."

Facebook has fully detailed exactly how the Beacon changes work:

- Stories about actions users take on external websites will continue to be presented to users at the top of their News Feed the next time they return to Facebook. These stories will now always be expanded on their home page so they can see and read them clearly.

- Users must click on "OK" in a new initial notification on their Facebook home page before the first Beacon story is published to their friends from each participating site. We recognize that users need to clearly understand Beacon before they first have a story published, and we will continue to refine this approach to give users choice.

- If a user does nothing with the initial notification on Facebook, it will hide after some duration without a story being published. When a user takes a future action on a Beacon site, it will reappear and display all the potential stories along with the opportunity to click "OK" to publish or click "Remove" to not publish.

- Users will have clear options in ongoing notifications to either delete or publish. No stories will be published if users navigate away from their home page. If they delay in making this decision, the notification will hide and they can make a decision at a later time.

- Clicking the "Help" link next to the story will take users to a full tutorial that explains exactly how Beacon works, with screenshots showing each step in the process.

This will be little comfort to Sean Lane, a Facebook user who's purchase of a Christmas present for his wife - a white gold diamond eternity ring - was displayed in his news feed without his permission for not only his wife, but his 220 other Facebook buddies to see.