4.0 SHARING INFORMATION
Social networks have revolutionised how we spread or share information.We can define social networks as virtual environments for communications,interaction and the sharing of resources.They can be divided into two groups:horizontal or general social networks and vertical or thematic social networks.

4.1 HORIZONTAL SOCIAL NETWORKS
The users of horizontal networks form communites who have diverse interests and a wide variety of reasons for using the application.The most popular are:

1. FACEBOOK:

This application allows groups of friends to publish both public and private messages with text,links,news,photos and videos.    

      2.TWITTER:

This social network has some anusual features.Users publish short text menssages(tweets) with no more than characters,which is called microblogging.One of the most interesting funtions is using hashtags to follow interesting events or topics.A twitter app is avaible for mobile devices.

      3.GOOGLE +:

this social network allows users to create circles of friends in order to share information.