Latest copyright battle: software pirates vs subversive programmers

Cars no longer steer, guns shoot off target or run out of
bullets, and footballs fly away into space.

Eventually the copy becomes so degraded
that the player -- in theory -- goes out and buys a legal version of the
game because he is so hooked.

It works by exploiting the systems for
error correction that computers use to cope with CD-ROMs or DVDs that have
become scratched.

Fade-protected software has fragments of
"subversive" software designed to look like scratches. These are arranged
in a subtle pattern on the disc, and are spotted by the game's master
programme, the report says.

If the master programme finds and
identifies these scratches, the game will play as usual. But if somebody
tries to copy the disc on a PC, the error-correcting routines built into
the computer fix the apparent scratches.

That means a "scratch-free" copy is
generated, and so will be spotted by the master programme as an
unauthorised copy. But instead of switching off the game, Fade allows it
to start up but subtly degrades it over time, in the hope of enticing the
gamer into buying a legit version.

"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,"
New Scientist says.

Macrovision intends to introduce the
technology in DVDs from next year, so that copied discs stop playing at a
key point in the movie's plot.