$BTC A Bitcoin miner will use his computer equipment to verify Alice's transaction and add it to the ledger. To stop miners from adding any transaction at will, they need to solve a complex puzzle. Only when a miner is able to solve this puzzle (called proof of work), which happens randomly, will he or she be able to add the transaction to the ledger and the record will be final.

Since running computer equipment requires capital expenditures, including the cost of the equipment and the cost of electricity, miners are rewarded with a new supply of Bitcoins. This is the monetary system behind Bitcoin, where the fees for verifying transactions on the network are paid by the person who wishes to make a transaction (in this case, Alice).

This makes the Bitcoin ledger resistant to fraud in a trustless manner. While it is resilient, the system still has some risks, such as a 51% attack, where miners control more than 51% of the total computing power, and there are also security risks that the Bitcoin protocol cannot control.