The FBI has joined efforts to track down those who took part of the computer code of one of the year's most highly anticipated games, Half-Life 2.
The much-anticipated game took five years to make
Federal agents mounted a dawn raid on a San Franciscan computer programmer last week, seizing hardware and software.
The programmer, Chris Toshok, detailed the events on his web log, denying any illegal activity himself.
The FBI declined to confirm or deny the raid, but US law enforcement sources indicated the search did take place.
The FBI action is the first sign of a serious criminal investigation following the appearance of part of the Half-Life 2 source code on the internet last year.
Doug Lombardi, a spokesperson for the developers Valve, told BBC News Online, "the Half-Life 2 Source code theft investigation is ongoing."
Valve said the blueprints to the game had been taken from its computers after a hacking effort in September.
As a result of the leaked top-secret code, which accounted for about a third of the game, the release of Half-Life 2 has been delayed twice. It is now due out in April.
Hungry for 'evidence'
The FBI operation appears to have been handled by the Seattle field office.
The agents were accompanied by US Secret Service representatives, according to Mr Toshok. They questioned him about a group known as the Hungry Programmers, with whom Mr Toshok previously shared a house, he said.
Mr Toshok alleged the agents who carried out the raid were armed with a search warrant, which he scanned and posted on his blog.
Half-Life 2 pits you against alien invaders
It stated they had permission to confiscate any computer equipment, software or documentation that "contain evidence or fruits or that are or were instrumentalities of criminal activity".
The search warrant was issued by the Northern Californian District Court, and included the name of a Seattle FBI agent. The San Franciscan District Attorney's Office also verified to the BBC the identity of the judge who signed the warrant.
If any warrant is issued by the District Court, it means the operation is an "exclusive FBI operation", the San Francisco Police Department indicated.
The warrant also specified the seizure of "any and all items and documentation, in whatever form, referring to, or relating to Valve Software, Half-Life, Half-Life 2, Team Fortress, Team Fortress 2, Counter Strike, and Condition Zero".
The numerous items listed on the seizure receipt which Mr Toshok said the agents gave him, included an Xbox with controller, several computers, plastic containers, CDs, cables and several hard drives.
Half-Life 2's developers were devastated when they realised key parts of code had been leaked on the net in September last year.
They appealed to millions of the game's devotees to help track down the culprits.
The leaked code included the physics engine which drives how the game's action is shown, as well as the sound system and other bits of code from various developers.
Half-Life 2 is the follow-up to one of the most lauded games ever and has taken over five years and teams of 30 developers to create.
The first release won several awards for its intelligent characters, plot and challenging puzzles.