A financial services firm is implementing a new policy to enhance the confidentiality and integrity of 'Restricted' client investment data. The data includes personally identifiable information (PII) and detailed investment records. Which of the following controls would BEST ensure that the data remains secure and is accessible only to authorized personnel?
Data encryption for both data at rest and data in transit.
Implementing network segmentation to isolate client data.
Applying strict file-level permissions on the client data files.
Maintaining detailed audit logs for all accesses to client data files.