Back in that day my brother and I both played on various MUDs (multi-user-dungeon/dimension). At the time most people had dial-up, due to my father's business we had an ISDN line and multiple computers, to prevent bots they made the assumption that multiple logins from the same IP were bots. So to combat this without blanket bans, the mods would warp us into a private area and have us type a different list of things simultaneously to satisfy themselves that we were actual people. It was a low-tech solution to a low-volume problem in a low-user-count game.
However, something similar like making the user do a captcha on each login or post if they're suspected of being a bot would be a low bar for a human to cross, but someone running a bot network would probably have to invest some time or resources into overcoming the captcha. (Mechanical Turk, machine learning, captcha farm, etc.)