Microsoft CEO Steve Ballmer has announced he will leave the company some time in the next twelve months, the man who oversaw many recent launches says his greatest regret was Windows Vista.

Insiders say the announcement could mean a large-scale management shake-up is on the way. The departure announcement comes at a significant transition for both the company and the industry as a whole, with many more people opting for mobile devices over traditional PCs, and Microsoft hedging its bets on a touch-optimised operating system designed to work across computers, tablets and smartphones.

In an interview over the weekend Ballmer said one thing sticks out as his main regret in the job he took over from Bill Gates.

“I would say probably the thing I regret most is the, what shall I call it, the loopedy-loo that we did that was sort of Longhorn to Vista,” Ballmer said, “I would say that's probably the thing I regret most. And, you know, there are side effects of that when you tie up a big team to do something that doesn't prove out to be as valuable.”

Ballmer says he is most proud of “the birth of intelligent personal computing” in the 1980s and '90s, and he has no idea what he will do in the next chapter of his life.