The FBI has arrested several people suspected of involvement in the theft of the source code for Half-Life 2.
Half-Life 2 promises more alien interaction
The involvement of the FBI came to light in January 2004 when dawn raids were carried out on suspects' homes.
Now arrests have been made in several countries but the FBI gave no details because its investigation is "ongoing".
The theft of the core code for the sequel to the hugely popular original came to light in October 2003 when it was posted online.
Half-Life 2 was originally due to be released on 30 September 2003 but nine months later still has no fixed release date.
The source code was stolen when malicious hackers broke in to the computer systems of Half-Life 2 developer Valve.
The thieves got hold of a playable demo version of the game that was originally shown off at the E3 trade show.
In e-mail messages posted to a Half-Life 2 fan website Gabe Newell, chief executive of Valve, speculated that the hackers got in by exploiting loopholes in Microsoft's Outlook.
The hackers who got hold of the code posted it online and it was widely shared via Usenet.
Valve enlisted the help of game fans to track down the thieves within days of it announcing that the theft had taken place and the game would be delayed as a result.
"It was extraordinary to watch how quickly and how cleverly gamers were able to unravel what are traditionally unsolvable problems for law enforcement related to this kind of cyber crime," said Mr Newell.
He said that Valve had been working with the police in several countries to prepare cases against the suspected thieves.
However, the FBI would not say when or where the arrests were made because it was still investigating the crime.
The raid in January was made on the home of San Francisco programmer Chris Toshok who detailed the event on his web journal or blog.
Mr Toshok denied any involvement in the theft but said he had shared a house with some members of the programming group, known as the Hungry Programmers.
Half-Life 2 continues the adventures of hapless lab assistant Gordon Freeman who battled foes from another dimension in the original game.