Bill Gates signs up for Twitter

Bill Gates currently has 70,000 followers on Twitter

Microsoft chairman Bill Gates has signed up for a Twitter account and has made his first tweets. Gates currently has over 70,000 followers, up from just 8,000 earlier this morning.

Gates is following just 40 people so far, including Microsoft, Unicef, Cern and US president Barack Obama.

"Thanks to you and all the other people who have welcomed me," he wrote today. "I've got a lot to learn about Twitter but look forward to sharing more. "

Gates has also rejoined social networking site Facebook, which he left last year complaining that it took up too much time.

He has posted links to Microsoft products, and pictures of visits to India and Africa for the Bill and Melinda Gates Foundation.