Fail-closed is the mode that ensures maximum security when a system component fails, as it does not allow any traffic through until the issue is resolved. This may disrupt normal business operations but is preferred in environments where security is more important than temporary downtime. 'Fail-open' would allow traffic to bypass the failed control, possibly leading to security breaches. 'Fail-soft' and 'Fail-secure' are not standard terms used to describe failure modes and could confuse test takers by suggesting other forms of failing mechanisms.