The DC did have copy protection, it would've made no sense to release a disc-based console in the late 90s without it considering CD burners were becoming ubiquitous (some early CD-based consoles like Sega CD didn't have copy protection because nobody really had the means to write CDs at home). Sega believed their proprietary GD-ROM format would prevent piracy, but ironically it was another format called MIL-CD Sega introduced with the DC that allowed it to be exploited and cracked games to be run without the need to modify the console. Info here.