Dictionary.net

/d[y]oop loop/ (also "dupe loop") [FidoNet] Aninfinite stream of duplicated, near-identical messages on aFidoNet echo, the only difference being unique or mangledidentification information applied by a faulty or incorrectlyconfigured system or network gateway, thus rendering dupkillers ineffective. If such a duplicate message eventuallyreaches a system through which it has already passed (with theoriginal identification information), all systems passed onthe way back to that system are said to be involved in a duploop.