**3.5 Smart contracts**

The "data" in the block can contain any kind of data. This includes copies of documents or software code. The software code may stipulate that when a certain event occurs, an action will be taken. For example, if the shipment is on board and the documents have been submitted to the blockchain and found to be correct, payment from the buyer to the seller should be made.

The oldest example of a smart contract is the vending machine: insert coins, choose a product, the product will be disbursed without human intervention.
