The best guard against the risk of attack by hackers is encryption. Encryption is the process of transforming data into an unreadable format using a secret key or algorithm. Encryption can protect data in transit and at rest from unauthorized access, modification, or disclosure by hackers. Encryption can also ensure the authenticity and integrity of data by using digital signatures or hashes.

Tunneling, message validation, and firewalls are not the best guards against the risk of attack by hackers. Tunneling is a technique that encapsulates one network protocol within another to create a secure connection between two endpoints. Message validation is a process that verifies the format, content, and origin of a message before accepting it. Firewalls are devices or software that filter network traffic based on predefined rules. These controls may help reduce the exposure or impact of hacker attacks, but they do not provide the same level of protection as encryption.