Microsoft has announced that chief executive Steve Ballmer will retire within the next 12 months, once it has found a successor.

Mr Ballmer is currently overseeing the transformation of Microsoft into a devices and services company.

He said in a statement: "There is never a perfect time for this type of transition, but now is the right time."

"We need a CEO who will be here longer term for this new direction," Mr Ballmer said.

once it has found a successor

Shares in Microsoft, criticised for its slow response to the booming market for mobile devices, leapt 9% on the news.