Social networking websites, where users meet others according to shared interests, are now the most visited sites on the Internet. Social networks (SNs) can be defined as "websites with profiles, semi-persistent public commentary on the profile, and a traversable publicly articulated social network displayed in relation to the profile". They are extremely popular among teenagers on the internet, via sites such as MySpace and Facebook. There are a number of specifically mobile SNs springing up, such as Dodgeball and Enpresence, which arguably pose more risks for children than internet based SNs, as they notify users when they are in physical proximity to their contacts. Meanwhile the existing web-based SNs are adding mobile services to their offering. Facebook, for instance, offers mobile browsing, photo uploads and the facility to exchange personal messages with other users via SMS (currently US-only) and MySpace is deploying similar services. Online 3D environments with some of the features of SNs (such as chat and messaging) where a player interacts with others using a character or avatar, are also becoming better known. Habbo Hotel, Neopets and Second Life are examples. However such environments lack the ‘profile’ aspect of typical SNs, although in some cases users may have virtual ‘homes’ where they can invite others to visit them. SNs are an easy way to stay in touch with many friends simultaneously, and to make new ones. They also stimulate users to learn how to use internet technologies and acquire basic HTML skills, in order to customise their profiles or "homes". | 
