An anonymous group has exploited a security loophole in the social networking site Facebook by 'hijacking' hundreds of groups.

Taking control of the Facebook groups allows them to change the name of the group, bombard members with messages and edit details. The 'hijackers,' who call themselves Control Your Info, insist they will not misuse the data; they want only to raise awareness of the dangers.

The group has discovered that if the administrator of a Facebook group leaves, any user can appoint themselves as a replacement. Hundreds of groups have been affected, all receiving the same warning: "Hello, we hereby announce that we have officially hijacked your Facebook group.

"This means we control a certain part of the information about you on Facebook. If we wanted we could make you appear in a bad way which could damage your image severly (sic).

"For example we could rename your group and call it something very inappropriate and nasty, like 'I support paedophile's rights'. But have no fear — we won't."

The renegade group's Web site claims the security side of social media has been "more or less neglected." Control Your Info has posted a YouTube video which warns that gaffes made in real life can be repaired, but "your online mistakes will be there forever."

Facebook said in a statement: "There has been no hacking and there is no confidential information at risk. The groups in question have been abandoned by their previous owners, which means any group member has the option to make themselves an administrator in order to continue communication to the group.

"Group administrators have no access to confidential information and group members can leave a group at any time. For small groups, administrators can simply edit a group name or info, moderate discussion, and message group members.

"The names of large groups cannot be changed nor can anyone message all members. In the rare instances when we find that a group has been changed inappropriately, we will disable the group, which is the action we plan for these groups."