Unfortunatly Raven/LA missed the opportunity to require a CD key that is checked upon attempt to join Internet multiplayer... While not a perfect protection, it does thin the heard for pirates. I know several people that pirate often but went and bought their own copies of HalfLife thanks to the WonID/CDkey check system they had.
But the game had no key, thus nothing is coded in to Identify the Installs. Now, weeks after release, it is too lat to impliment any thing of this sort