Dup Killer /d[y]oop Kill'r/ N.
[FidoNet] Software That Is
Supposed To Detect And Delete Duplicates Of A Message That May Have
Reached The FidoNet System Via Different Routes.
dup loop: /d[y]oop loop/ (also `dupe loop') [FidoNet] n. An
infinite stream of duplicated, near-identical messages on a FidoNet
{echo}, the only difference being unique or mangled identification
information applied by a faulty or incorrectly configured system or
network gateway, thus rendering {dup killer}s ineffective....