The Jyn exploit is the use of an alt flag (or cooperating friendly flag) to drop a war chest on an island in order to make a blockade sinking without incurring a war with the actual attackers. This works on the premise that the defender only needs to declare war against one attacking party (i.e. the alt flag or the friendly flag) to make the entire blockade sinking. The tactic is named after Jyn, the Looterati Minister of War.
The Jyn exploit was first used at Eta II by Silver Dawn to repel Silver Dusk. Because Silver Dawn used the flag Merciless Exploit of War (MEOW) the Jyn Exploit is frequently called the MEOW Exploit. The tactic was also used by Excalibur, an alt flag of Avalon in the blockade of Spring III.
The implementation of fame requirements for attacking flags made the Jyn exploit less straightfoward.