Originating from W77 they spread like a disease to other worlds/servers to 'crash' (cause so much damage to the boss that only W77 can get the items after the boss dies).
This destroys an innocent persons fun/enjoyment as it can take up to an hour to find a free/empty server and forces them to leave as they cannot compete with the large clan 'crashing' them.
Runescape is owned by Jagex Ltd.
Person 2: "Awh... I hate them so much, they always crash me and I can never get loot, I hope Jagex ban them!".
Person 1: "Yeah... I'll bring some maxed out players next time to beat them- darn noobs".