What security measure should be taken for storing clients' government-issued ID numbers?

The most effective security measure for storing clients' government-issued ID numbers is to encrypt the government ID field with Classic Encryption. Encrypting sensitive personal data, such as government-issued IDs, is crucial for protecting that information from unauthorized access. It ensures that even if data is intercepted or if someone gains access to the database, they cannot easily read or misuse the ID numbers without the appropriate decryption keys.

Encryption provides a layer of security that goes beyond basic visibility controls. While restricting visibility (removing it from page layouts or changing organization-wide defaults to private) helps limit who can see the data, it does not protect against potential data breaches or exposure. Two-factor authentication is a good security practice for logging into systems but does not directly protect the stored data itself.

In summary, encrypting sensitive information is a fundamental practice in data security that helps to safeguard clients' governmental ID numbers against unauthorized access, thus making it the best option among the available choices.