is this possible???

ok listen i just got on WoWLegacy and i've already seen some buggers or hackers i don't really know what are they.
the exploit is like this: The abuser is nacked and wielding a 2H sword, when he attacks it's instant kill..
So if anyone knows how can it be done please post in here
thanks

Either attack stacking as in hiting the enemy like 20000 times in a second, or a form of lag attacks, you can hack some players ip so they have like 21000 thousand ms or stuff like that, real annoying hack i remember this damn mage did that shit to me