Furnace dupe (fixed).

Furnace dupe (fixed).

The furnace dupe is probably the most famous dupe in Minecraft Beta 1.7.3. It involves placing the desired item in the furnace, then closing the furnace inventory, enabling FreeCam in the cheat client, as well as the instant block destruction feature, flying to the furnace in FreeCam, clicking on it (thus triggering its destruction), then quickly opening the furnace inventory, waiting for the furnace to destroy itself, and receiving an infinite item!

Dupe process.
Watch the demonstration video here.

This dupe has long been fixed on 2Beta2T, but its consequences almost completely destroyed the server's economy. However, everything will probably recover over time.

Furthermore, the chest dupe works similarly - the only difference is the capacity in which we place the desired item.