The social networking Internet site Twitter hit a milestone Saturday when a Japanese user sent the 20 billionth tweet.

The user ("GGGGGGO--Lets--Go") is a graphic designer in Tokyo.  He was immediately inundated with congratulatory messages from around the world.

While it took Twitter four years to reach tweet number 10 billion in March of this year, it took less than five months to double the figure thanks to its increasing worldwide popularity.

Twitter allows users to send out very brief messages to others on the Internet.

Users interested in a particular topic, say a music group or a political issue, for example, can search the site to find what other people are saying on the subject.

The messages, called "tweets," are limited to 140 characters.  

Some information for this report provided by AP.