Twitter

Twitter is a popular micro-blogging service launched in 2006 which has rapidly grown to become one of the most popular sites on the internet.

The service revolves around messages called Tweets, which are restricted to 140 characters. This limitation appears to derive from the service allowing users to send a Tweet from a mobile phone using SMS.

Tweets are delivered to each users' followers, which are other users who have selected to receive updates from that person.

Twitter is now becoming a central part of many companies' social media strategies and a popular means of disseminating information.

It has also has been used in many political events, such as the recent civil unrest in Iran, Egypt and Morocco, to coordinate demonstrations and share information with the outside world, leading to the site being taken offline in such countries on several occasions.

The site has often targeted by cyber attackers too, most notably the Iranian Cyber Army, which overtook the site in December 2009.