With a number of anti x-ray plugins that focus on the number of diamonds/ore mined within a certain time frame I figured this might be even more useful and more lightweight. As many x-rayers in a PvP/Survival environment are actually more interested in bases/chests than finding ores, often they use x-mods and texture packs as the walk the world's surface, when they see caves or rooms below, specifically lit with torches or even uncovered/unhidden chests, they whip out their pickaxe and dig straight down to their prize. A simple plugin that monitors player's block break events for straight, downward pillars of say 10 (configurable) blocks or more and alerts admins in-game so that they could investigate and saves a log for later review (go to location of down-pillar, check results with logblock/big brother) in case admins are not online. In my experience this has been the hallmark signature of an x-rayer. Most players who are playing legit will staircase down because they can't see potential falls and/or lava below them, so a stair down is safer. X-rayers are confident to just dig straight down. If the pillar down is to a chest of a bed of ores, bingo you've caught one.
