Former Microsoft chief executive Steve Ballmer disclosed today that he has taken a four percent stake in Twitter, expressing confidence in the messaging platform's new management team. Ballmer, who last year left the US software giant and then became owner of the Los Angeles Clippers NBA team, announced the stake in a tweet as he offered praise for newly returned Twitter CEO Jack Dorsey. "Good job @twitter, @twittermoments innovation, @jack Ceo, leaner, more focused. Glad I bought 4% past few months," Ballmer said in his tweet. The stake in Twitter by Ballmer, whose Microsoft investments make him among the world's wealthiest individuals with a fortune estimated by Forbes at $22.8 billion, would be worth some $800 million at current share prices. Twitter shares have risen some 25 percent this month as Dorsey was named CEO on a permanent basis. Twitter also announced a reorganization that cut eight percent of its staff and introduced a new Moments features that offers real-time news. Last week, Ballmer lauded Twitter and Dorsey shortly after the co-founder's appointment was announced. "I think @twitter is remarkable," Ballmer said at the time. "There is amazing chance to innovate and grow. Excited to see progress with @jack as CEO Impressive dude!" Ballmer becomes one of the largest stakeholders in Twitter, ahead of Dorsey's three percent but behind Saudi billionaire Al-Waleed bin Talal's five percent and co-founder Evan Williams' seven percent.