Which of the following is NOT a characteristic of smart contracts?

Smart contracts are self-executing contracts with the terms of the agreement directly written into lines of code.

The characteristic that they always run safely on the network is not accurate. While smart contracts are designed to be executed automatically in a secure manner, they can be vulnerable to security risks and bugs in the code. The decentralized nature of blockchain helps to reduce certain risks, but it doesn't inherently guarantee that every execution will be free from potential exploits or errors. There are numerous examples of smart contracts being hacked or compromised due to flaws in their code or unforeseen interactions with other contracts.

The other characteristics mentioned highlight aspects of smart contracts that are indeed true. For instance, they can be deployed dynamically by anyone with the appropriate permissions, they can run concurrently which allows multiple executions at the same time, and their code can come from untrusted sources, necessitating the need for careful auditing and testing before deployment.