Chief operating officer Stephen Elop is leaving Juniper Networks Inc. (NYSE: JNPR), a move being announced almost exactly one year after his arrival.

In a Securities and Exchange Commission (SEC) filing, Juniper said COO Stephen Elop turned in his resignation January 9. Elop had been hired by Juniper on January 8, 2007. (See Juniper Revives COO's Office.)

Elop is headed for Microsoft Corp. (Nasdaq: MSFT) to run its business division, which includes the ubiquitous Office suite. He's replacing Jeff Raikes, who announced that he'll retire from Microsoft in September. (See Microsoft Hires Juniper Exec.)

Microsoft says Elop will join in late January and work with Raikes during a transition period.

A Juniper spokesman says the company is "actively recruiting" for a replacement COO.

Elop's roots are closer to PCs than telcos. He was the final chief executive of Macromedia, overseeing its acquisition by Adobe Systems Inc. (Nasdaq: ADBE) in 2005.

At Juniper, Elop was handed responsibility for areas including sales, manufacturing, marketing, and all product groups. He was the first COO at Juniper since 2003, although Jim Dolce, former CEO of the acquired Unisphere Networks, handled some COO-like tasks before leaving Juniper in 2006. (See Dolce & Others out at Juniper and Dolce Starts Verivue .)

Separately, Juniper lost a board member this week: former Siebel Systems Inc. (Nasdaq: SEBL) CFO Kenneth Goldman, who'd been appointed in 2003. (See Juniper Hires Director.) Goldman resigned January 7 because he'd taken a job at a Juniper competitor, according to an SEC filing.

— Craig Matsumoto, West Coast Editor, Light Reading