Explanation:
Screened subnets are demilitarized zones (DMZs) and are oriented toward preventing attacks on an internal network by external users. The policies and procedures to classify information will ultimately result in better protection but they will not prevent actual modification. Role-based access controls would help ensure that users only had access to files and systems appropriate for their job role. Intrusion detection systems (IDS) are useful to detect invalid attempts but they will not prevent attempts.