Which security measure helps protect against unauthorized physical access to systems?

Access control systems are crucial for protecting against unauthorized physical access to systems. These systems are designed to regulate who can enter certain areas or access specific resources within an organization. They typically utilize various methods, such as keycards, biometric scanners, or pin codes, to ensure that only authorized personnel are able to gain entry into secured environments.

By implementing access control systems, organizations can significantly minimize the risk of unauthorized individuals gaining physical access to sensitive areas where critical infrastructure, equipment, and data might be housed. This not only helps in preventing potential theft or tampering but also protects the integrity and confidentiality of the organization's information systems.

In contrast, the other options primarily address different aspects of cybersecurity. Firewalls focus on network traffic and preventing unauthorized network access; antivirus software protects against malware and malicious software attacks; while data encryption secures information by making it unreadable to unauthorized users. These measures are essential for information security, but they do not directly address physical security concerns.