Microsoft Corp. on Wednesday said Kevin Johnson, the executive in charge of its Windows and Web operations and an instrumental player in the company's failed $47.5 billion bid to buy Yahoo Inc., is leaving the company.

After a short transition, Johnson will step into the role of chief executive officer at Juniper Networks Inc., a networking hardware maker, according to a person familiar with the situation.

The person asked not to be named because Juniper had not yet announced Johnson's appointment.

Johnson has served since 2005 as president of Microsoft's platforms and services division, which included the Windows operating system and Windows Live programs such as Web e-mail and instant messaging. The division also included online advertising, search and Microsoft's MSN sites.

Johnson, who joined Microsoft in 1992, has been the public face for the company's search and online advertising strategy, meant to help the company catch market leader Google Inc., since starting the job.

It was Johnson who laid out Microsoft's aggressive goals last November that included capturing 30 percent of U.S. search queries.

Over the last year, as it became clear that Microsoft's internal search and advertising efforts were not propelling the company forward fast enough, Johnson was at Chief Executive Officer Steve Ballmer's side while Microsoft attempted to buy Yahoo outright and, when that failed, to buy the Silicon Valley icon's search operations.

He also spearheaded the $6 billion acquisition of online advertising company aQuantive in 2007. Incorporating aQuantive has boosted Microsoft's Web ad revenue, but not enough to put the software maker in league with leader Google Inc.

"Whether it was his decision to leave, or whether it was based on recent events probably related to Yahoo and the online segment's last-quarter performance, I don't know," said Matt Rosoff, an analyst for the independent research group Directions on Microsoft.

Last week, Microsoft said its online business lost $488 million in the quarter, more than double its year-ago loss, and announced hundreds of millions of new spending to try to turn the operations around.

Rosoff said the fact that a Yahoo deal has still not come to fruition was probably one reason why he's leaving _ voluntarily or not.

"That had to be a pretty frustrating process to go through," he said.

Microsoft says the platforms and services division will now be split in two, with heads of the groups reporting directly to Ballmer.

The newly formed Windows/Windows Live division will be led by senior vice presidents Steven Sinofsky, Jon DeVaan and Bill Veghte.

Microsoft said it will search for a new sole leader for its online services business. In the interim, senior vice presidents Satya Nadella and Brian McAndrews will remain in the lead of engineering and advertiser and publisher solutions.