To block imported games, Sega slightly altered the shape of the cartridge slot between regions, although it kept the same pinouts. Games could also perform 'region locking' by checking the value of the Version register, which outputs the console's region code.
There were two simple ways to bypass this: purchasing a third-party cartridge converter or disassembling the console and bridging the pins on the motherboard to alter the value of the Version register.
When it comes to software anti-piracy measures, the easiest check involved verifying the SRAM size. Bootleg cartridges often bundled more space than needed to fit any title, so games checked for the expected size during startup. Programmers could also implement extra checksum checks at random points in the game to counteract attempts to bypass the initial SRAM checks. The only way to defeat this was to painstakingly find all the checks and remove them one by one...