Illegally copied games protected by the system work properly at first, but start to fall apart after the player has had just enough time to get hooked. As a result, the pirated discs actually encourage people to buy the genuine software, the developers say.
The new protection system, called Fade, is being introduced by Macrovision and the British games developer Codemasters.
It makes unauthorised copies of games slowly degrade, so that cars no long steer, guns cannot be aimed and footballs fly away into space. But by that time the player has become addicted to the game.
Fade exploits the systems for error correction that computers use to cope with CD-ROMs or DVDs that have become scratched. Software protected by Fade contains fragments of "subversive" code designed to seem like scratches. The bogus scratches are arranged on the disc in a subtle pattern that the game's master program looks for. If it finds them, the game plays as usual.
When someone tries to copy the disc on a PC, however, the error-correcting routines built into the computer attempt to fix the bogus scratches. When the copied disc is played, the master program then cannot find the pattern it is looking for, so it knows the disc is a copy.
What happens next turns the usual rules of software protection on their head. Instead of switching off the game and preventing it from playing at all, the master program begins to disable it. In the game Operation Flashpoint, which has been the proving ground for Fade, players soon find that their guns shoot off target and run out of bullets.
"The beauty of this is that the degrading copy becomes a sales promotion tool. People go out and buy an original version," claims Bruce Everiss of Codemasters.
Following its success with Operation Flashpoint, Codemasters is also using Fade with a new snooker game. Copies play normally for a while, but after a predetermined number of potshots, gravity is progressively turned off so the balls start behaving oddly and end up floating over the table.
Fade was devised by Richard Darling, who founded Codemasters 16 years ago, and has now been included in Macrovision's SafeDisc anti-piracy system. Next year, Macrovision plans to release a DVD movie protection system called SafeDVD, which will use a similar technique to make copied discs stop playing at a key point in the movie's plot.