Expanding its presence in the area, Sony's video-game arm has acquired Zipper Interactive, a Redmond-based studio best known for the "Socom" game franchise.

The two have been long-term partners since 1999, when Zipper began developing the first military-themed "Socom" game. Financial terms were not announced.

Being acquired removes some risk for Zipper as it creates more expensive and complex games for Sony's next-generation video-game console, said Brian Soderberg, who co-founded the studio in 1995.

The studio has about 130 employees and is expected to hire more for next-generation games.

"Zipper has grown to big teams doing business with Sony," Soderberg said.

"It was great for us to grow that large. At the same time, it was a bit risky because all of our eggs were in one basket with Sony."

Even before the acquisition, Zipper operated in many ways like one of Sony's in-house teams. It used Sony's resources, and Sony marketed its games worldwide.

But Zipper kept some secrets, including components of its video-game engine. Now, it will share that information, Soderberg said.

Zipper made a name for itself when the original "Socom" became Sony's first venture into online console gaming.

The $60 game debuted in 2002 with a device that enabled online play on the PlayStation 2, and would eventually sell about 3.5 million copies.

Zipper debuted a sequel to "Socom" in 2003 and a third game last year, along with a version for Sony's PSP handheld system.

It's now working on several titles, with an eye on the PlayStation 3 console due out later this year.

Soderberg and co-founder Jim Bosler will continue to manage the studio, and no layoffs are expected.

Sony's other projects in the area are also growing. An arm of Sony Pictures opened an online-games studio in Bellevue about a year ago; that office now has about 50 employees, including several ex-Microsoft game creators.

The studio is working on an as-yet-unannounced game that is expected to be significant in the genre of so-called massively multiplayer online games, which generally involve a vast virtual world in which players interact with each other over the Internet.

Sony also works closely with Sucker Punch Productions, a Bellevue studio that has developed three games in the "Sly Cooper" franchise exclusively for the PlayStation 2.

Kim Peterson: 206-464-2360 or kpeterson@seattletimes.com