IOTA uses PoW for spam protection, similar in spirit to the PoW used in Hashcash. This is a short computational operation, which should not be confused with the expensive PoW employed in miner-based ledgers such as Bitcoin.
The difficulty of the PoW is set by a variable called Minimum Weight Magnitude (MWM). This refers to the number of trailing zeros (in trits) in transaction hash. MWM is proportional to the difficulty of the Proof of Work.
The device which does the PoW will bruteforce the transaction hash to find a `nonce` that has the correct number of trailing 0's. Every extra trailing zero to be found will increase the difficulty of PoW by 3 times.
- Mainnet MWM parameter: 14
- Testnet MWM parameter: 9