Arrests have been made in the theft of computer code behind Half-Life 2, which is expected to be one of this year's best-selling titles, the game's manufacturer announced yesterday.

The theft last year had a role in the delayed delivery of the game, originally scheduled for release in September 2003, as Valve Corp., based in Bellevue, Wash., rewrote parts of its programming and assisted in an FBI-led investigation. Valve chief executive Gabe Newell said at the time that he believed the code was stolen by hackers from a company computer.

Half-Life, the game's predecessor, has sold more than 8 million copies since being released in 1998; the game marked Valve's debut, and it remains a cornerstone of the company's business. The sequel is now scheduled for release this summer.

The FBI-led Northwest Cyber Crime Task Force, which conducted the investigation, declined to say how many arrests were made or where they were made, and did not make public any other details, citing an ongoing investigation. The company said arrests were made in "several countries."

In a statement, Valve said that it had received thousands of tips related to the theft. Founder Newell credited a "core group" of the company's customers for sending and analyzing information that helped lead to the arrests.

"Gamers were able to unravel what are traditionally unsolvable problems for law enforcement related to this kind of cyber-crime," he said.

Half-Life, a "shooter" game, featured as its main character scientist Gordon Freeman, fighting against extra-dimensional aliens and dark U.S. government forces -- led by an evil figure known as "the G-man" -- in an underground government facility.

Half-Life's sequel is anticipated enough that some computer makers expect business to surge when the game reaches retail shelves. Cutting-edge games can drive many fans to upgrade their systems so that the game software looks and performs as impressively as possible.

Frank Azor, vice president of worldwide product marketing at Alienware Corp., a maker of high-end computers for hard-core gamers, said the game's delay has had some impact on sales as gamers have put off upgrading their machines. "Man, we were hoping that game was going to come out at the end of last year," he said.

Game-making software developers yesterday expressed hope that law enforcement agencies have caught the thieves.

"It's certainly a nightmare scenario for any studio owner like me," said Brian Reynolds, president of Big Huge Games Inc. in Timonium.

Security precautions are highly important for game developers, who spend years and millions of dollars designing titles. When Reynolds's shop was in the early stages of testing the online features of its latest game, Rise of Nations, the company put a few computers outside the bounds of the firm's security apparatus. Reynolds was amazed by how quickly the Internet-connected machines became riddled with malicious software.

"They spent a few hours outside the firewall and they were toast," he said. "We had to flatten them." Reynolds does not think the systems were specifically targeted in an attempt to steal his company's intellectual property.

Though hard-core gamers and hackers share some of the same obsessions, some in the gaming community say the delay of Half-Life 2 has caused something of a backlash against hackers.

"Gamers really want to play Half Life 2, and they really, really resented the delay," said Vince Broady, founder of video-game news Web site GameSpot, in an e-mail.

Darrin Schrader, one such gamer, agreed. Schrader was a fan of Half-Life, particularly an online version of the game called CounterStrike, until people using hacker-designed tools started joining the games and using software that gave them an unfair advantage.

"It hurts the community when people do this," he said. "I just hate cheaters, and hackers are cheaters."