Which of the following is considered an efficient security tool for organizations?

An email digital signature certificate is considered an efficient security tool for organizations because it provides a means of ensuring the authenticity and integrity of email communications. When a digital signature is applied to an email, it verifies that the message has not been altered in transit and confirms the identity of the sender. This is particularly important in maintaining trust within email communications, as it helps prevent email spoofing and phishing attacks, which can lead to data breaches and other security incidents.

On the other hand, while the other options also contribute to security measures within an organization, they each serve specific purposes. For example, a firewall is primarily focused on network traffic control, antivirus software protects against malware, and regular password changes are part of a broader strategy to enhance account security. However, none of these tools, on their own, provides the same level of assurance regarding the authenticity of communications that a digital signature certificate does.