I haven't had this happen while farming atma yet, but I've had two people just randomly out of the blue come up to me with a handful of mobs and try and mpk me while I was leveling fishing. The first one I yelled at the dude and he used the excuse that they were lagging even tho he ran the mobs right up to me, ran around me with them for a few and when he was close to dying he ran off quick to lose threat but almost killing me. 2nd time was today where some monk came up to me while I was in Mor fishing and he stands there pulling the snakes over to try and hit me. To which I just got up, mounted and moved away and he ported out when I left the spot. XD