Duplication glitch

The party hat duplication glitch was the most famous glitch of RSC, exploited on 7 November 2003. Its effects continue to have an impact on the economy.

Execution
The glitch was not an attempt to duplicate items. A player had been experimenting with RuneScape by using a third-party program in an attempt to simply trade the scythe. Although the player never managed to trade the scythe, he did discover how to create any non-stackable item. Therefore, the glitch did not duplicate existing items but instead created new ones.

In his excitement, the experimenter revealed to very few people how to execute the glitch. These players then duplicated several items, the most expensive at the time: specifically party hats, rune two-handed swords, and dragon square shields. The most expensive item, the purple party hat, was created most amongst them. That day, though, one of these people revealed that the glitch existed. However, he did not reveal how to perform it.

Effects
Jagex banned all the players who had abused the glitch, and deleted some party hats. However, since the duplicated hats carried no identifiable marks, many remained in circulation as Jagex could not be sure whether any specific hat was from the drop or was new. Jagex did not roll back the servers, so the most expensive party hat dropped to the least expensive. The purple party hat remains the least expensive today.