I think the term gank came from Ultima Online? Read it somewhere, and that was definitely the first place I came across it, and the first big MMORPG. There, it was basically short for 'para gank'. Mages had a spell that paralysed people, but it only lasted like 2 seconds longer than it took to recover from casting the spell. But with some friends, the mage could just do that over and over while everyone else hit the paralysed guy. Ultima was way harsher than here. A gank in UO would be three hidden players all firing a crossbow bolt at you at once, appearing in the same instant that you die, and then disappearing instantly again. Or more likely, going to your corpse and taking all your items and everything you ever owned, and laughing at your little ghost running away.
But yeah, think it came from UO, which was a brutal MMO, although it was, at least in the beginning, in roleplay. It was basically more about the surprise/lack of ability to defend than the numbers. That's less of an issue here because combat takes five hours and all ships have ten billion hitpoints.
