Weapons diversion is the movement of arms from lawful or military control into illegal markets. It usually happens when custody breaks down: inventories are incomplete, storage is weak, corruption is present, or transport is hard to verify. Once an item leaves controlled custody, it can be resold, cached, or passed through criminal transport networks with little traceability.
In cyber security, the term matters because arms trafficking increasingly depends on the same control problems that affect digital supply chains: weak provenance, poor logging, and gaps in chain of custody. Defenders use strict inventory management, serial-number tracking, auditing, border screening, and post-conflict tracing to reduce diversion. Attackers benefit when those controls fail, because diverted weapons can equip organized crime, armed groups, or coercive operations that overlap with cyber-enabled fraud, extortion, and smuggling.