there are always ways to combat cheating, however when you stop one they will find another way, so is it worth the hassle spending time trying to fight against it.
Once you are adept at finding the cheaters it becomes easier to police it, if you fix a cheating bug then you have to start all over again trying to figure out how you can spot whatever new cheat they have used
If you can figure out who is cheating on your server simply kick them off
In answer to this specific cheat then i believe the only way is to have all your server members have all their missions in the mpmissions cache folder and not the mp missions folder, then the admin runs the following line while in briefing
#debug checkfile MPMissionsCache/missionname.pbo
This also requires that the mission-filename doesn't contain any spaces, which makes the filecheck fail, without reporting anything.
This is a workaround until BIS has a better solution for it.
anybody that had a different version of the map would then throw up an error
(I aint gonna explain how the cheat works as that would be downright stupid, but thats basically it, by the way this cheat has been around for ages
i dont know what happens if there are two mission files, one in each folder