In October 2010 Facebook adjusted some privacy features and one of these changes was an amendment to the Groups function.
Traditionally there are 3 types of groups available to be created in Facebook :
Open Groups – were open to all Facebook members to join as they wish and to recommend to friends to join if they would wish too.
Closed Groups – are groups that once created by the owner/administrators can only be joined after the owner/administrators confirm an application request.
Secret Groups – are hidden to the Facebook community and only found if the owner/administrators or a member invites a user directly. Hidden groups are not shown in any searches either on Facebook, or search engines like Google and Bing.
Facebook changed the membership option on Open Groups to automatically add users that have been recommended by their friends to that particular group; instead of requiring them to click the “Join Group” button.
This obviously creates a massive security hole that can be used by spammers and malicious users and also accidentally by legitimate users in lots of ways. Take the example that a someone is known to be flying to the USA and some friends decide to play a joke on him and automatically add him to a group that could be linked to or seem to support terrorist activity in some way. Not only will this flag that traveller on all sorts watchlists; but its fair to say that their arrival at US Border Control will not be the sort of treatment and questioning that they would have expected.
At present there is no way to “opt-out” of this scenario happening in the first instance, until Facebook change this security flaw. Only your friends can add you to a group. Once you have been added, (this will be shown on your wall and in the public timeline) you can remove yourself from the group – and cannot be added back into it by any of your other friends. But unfortunately, this still does not stop the messaged being publicised to the world that you are are now a member of “Group XYZ”.
So this is another reason to watch who you add as friends on Facebook.