Chunks of the code for Half-Life 2 has been officially released online.
Steam members can pre-load some of the code for the game
The long-awaited sequel has no official release date, but game maker Valve has started letting members of its online community get hold of encrypted copies.
When officially launched, downloaders will be able to buy codes to access the encrypted files and start playing immediately.
But Valve is facing criticism online for making the game available, but not actually letting people play it.
Waiting to play
The 500MB compressed file containing some of the encrypted game was put on machines serving Valve's Steam community on 26 August.
Unpacked the file is reportedly about 1GB in size.
Steam is software that, among other things, lets players take each other on in online games, acts as an anti-cheating and online authentication system and helps people get hold of the latest updates.
Half-Life 2 was originally supposed to appear in September 2003 but has faced consistent delays.
Quake creators tried to protect their game too
Even now no fixed date has been given for its release and some gamers speculate that it may not appear until November.
Others believe that release is imminent because Valve is happy for the game software to be downloaded.
Some also speculate that the relatively small size of the files means that the encrypted version is not the full game. Many expect to have to download more code when the full and final game is released.
According to some reports, the download only includes files such as textures and audio, rather than the actual levels and programs needed to run the game.
A lot of people keen to download the game are been forced to wait because the Steam servers are managing the numbers of people allowed to download it at any one time.
However, soon after being appearing on the Steam servers, copies of the download started to appear on the BitTorrent file-sharing network.
In the past when other game makers have tried similar tactics, they have gone badly wrong.
Id Software's shareware version of Quake contained the full game but only let players try out the opening levels for free.
To play the full game, players were supposed to buy a code to unlock it.
Instead hacks for the protected parts of the game were found and many people bought those instead of the official codes and played the whole game without paying for it.
Many people commenting on the Half-Life 2 release on the Slashdot discussion boards criticised Valve for keeping the game locked up even though it was almost ready to play.