Microsoft's Platforms and Services head has jumped ship to become CEO of Juniper Networks.
Kevin Johnson will arrive at Juniper in September. At Microsoft, he was in charge of Redmond's Windows and online businesses.
Johnson played a key role in Microsoft's recent failed attempt to take over Yahoo, as part of the company's strategy to grow its online business, and catch up with Google.
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Scott Kriens, current Juniper chairman and CEO, will continue as chairman and "will remain active in the areas of strategy and leadership development", said Juniper.
"I am delighted to join Juniper," said Johnson. "Juniper is a company with a clear technology agenda, great talent and an amazing growth opportunity in a growing industry. I'm looking forward to bringing my experiences to help Juniper scale and deliver great value to Juniper's customers, partners, employees and shareholders."
Johnson was responsible for the launch of Windows Vista, after extensive delays in the product, and oversaw a Microsoft online business which has seen operating losses spiral.
The official announcement of Johnson's move to Juniper was preceded by Microsoft announcing that it would be splitting up his Platform and Services division.
The new groups will now be Windows/Windows Live and Online Services, with both reporting directly to Microsoft CEO Steve Ballmer.