Facebook's location-sharing service, Places, has started rolling out across the UK, the social-networking company announced on Friday.
The geolocation service — which was introduced in the US on 18 August and launched the following day — invites users to 'check in' to certain locations to share their movements with friends. As with location-aware services such as FourSquare, these check-in spots include businesses and places of interest.
Accessible via an iPhone application or on the web via touch.facebook.com, Places also gives people the option of checking-in their friends, if permission has been granted in their privacy settings. Users under the age of 18 are restricted to allowing only friends to view their check-ins.
"Privacy is really important to us... There are clear privacy settings to give people control over who can see where you have 'checked in'. The default for the majority of people will be 'friends only' for this setting," Facebook said in a statement.
The service is opt-in only, and users can also delete check-ins or choose to remove themselves from the 'People Here Now' list after having checked in at a location.
Rik Ferguson, senior security advisor at Trend Micro, said that the ability to check in friends poses a potential problem.
"Even if you have set your location to be visible to 'friends only', Facebook will allow anyone else checked-in nearby to see your location. That doesn't sound ideal to me, and could represent valuable information to someone with less than honourable intent," Ferguson said in a statement.
"Friends can check you in anywhere, regardless of your actual location. Once you have tagged another user in your check-in, they receive a notification along with the option to remove the tag; but from the moment they are tagged, the information is posted on Facebook — without their consent," he added.
Ferguson suggested the system should be changed to make sure that the information does not become public until it has been agreed by all the people concerned. This could help reduce the "massive risk to individual privacy". In August, web-analytics firm Hitwise said that Facebook accounted for one in six pages seen by UK internet users in a single month.
The risks in revealing movements via geolocation services such FourSquare and via social networks such as Twitter have been highlighted by security experts and by sites such as PleaseRobMe.com, which warn that burglars could use such information to identify potential victims. Police in New Hampshire recently arrested three suspected burglars who allegedly used social-networking sites such as Facebook to find people who would not be home at a certain time.
Facebook told ZDNet UK that Android and BlackBerry versions of the Places app are currently being developed, but that there is no release timeline as yet.