[quote="Firebrand":20uonmd3]Why would registered Doom be illegal? AFAIK the ultimate Doom was a special version of Doom and was sold as the original game too.
EDIT: Only Doom II had a pirated version of the game that couldn't be patched to the latest version.
Well it said the original three episode doom, not ultimate doom, is illegal when bought in stores in all countries except a few of them. It says it in Hank Leukart's FAQ that comes with the doom demo.