Microsoft chief executive Steve Ballmer announces retirement

Microsoft chief executive Steve Ballmer is to retire from the technology giant within the next 12 months.

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

Mr Ballmer, who last month unveiled a restructuring to address the criticism, said in a statement: "There is never a perfect time for this type of transition, but now is the right time."

Rory Cellan-Jones reports.