The stated reason for the way World of Warcraft: Classic was built upon the modern client architecture was to reduce any chance of exploits, but “reduce” is not the same as “eliminate.” Sure enough, a rather nasty exploit was found allowing players to repeatedly farm any given enemy in a dungeon without resetting the instance, allowing for chain-killing even the final boss of a dungeon without even slowing down to clear the rest of the enemies. The exploit is being patched out today, thankfully.
Players who used the exploit shouldn’t be getting comfortable with a shrug and a “well, the good times are over” attitude, either; the announcement of the hotfix includes a promise that those who exploited the bug will receive appropriate punitive measures, likely including a removal of items at the minimum. While there’s always some measure of defense for ambiguous situations when it comes to exploits, we tend to doubt that anyone “accidentally” killed the final boss a dozen times without fighting anything else.
In less punitive news, players are working to put together a census of the population on WoW Classic, a task made more difficult by the lack of an Armory connection but not impossible. It’s a census purely of characters rather than players, of course, but it is the beginning of tracking activity.