One Minecraft server I played on installed a program for blocking x-ray hackers (a type of hack that lets you see valuable ores through walls so you know exactly where to mine).

The anti-xray mod worked by reporting to the user that the blocks behind a wall are a jumble of completely random blocks, preventing X-ray from revealing anything meaningful.

This mod resulted in massive lag, because when you are mining, every time you break a block, the server now needs to report that the blocks behind it are now something different. It basically made the game unplayable.

The server removed the mod and switched to having moderators use a different type of x-ray mod to look at the paths people mine in the ground. Those using x-ray hacks would have very suspicious looking mines, digging directly from one vein to another, resulting in erratic caves. Normal mining results in more regular patterns, like long straight lines or grids, where the strat is to reveal all blocks in an area while breaking as few as possible.

Once moderators started banning people with suspicious mining patterns, hacking basically stopped.

It’s possible to still hack and avoid the mods in this kind of system by making your mines deliberately look like legitimate patterns, but then the hacker is at best only slightly more efficient than a non-hacker would be.