Which activity category involves implementing barriers to block unauthorized access?

The correct activity category that involves implementing barriers to block unauthorized access is access control. Access control is a fundamental aspect of security management that ensures only authorized individuals can access specific data or systems. It encompasses a range of strategies and technologies, such as user authentication, permissions, and physical barriers, designed to safeguard sensitive information from unauthorized users.

This concept is crucial in information security since it directly impacts the confidentiality, integrity, and availability of data. Effective access control measures help to mitigate risks associated with data breaches and unauthorized access, thereby protecting the organization's assets and maintaining regulatory compliance.

While obstacles and prevention might seem related, it is a broader term that does not specifically focus on the mechanisms used to permit or restrict access. Surveillance and notification pertain more to monitoring activities and alerting relevant parties, and response and recovery focus on handling incidents after they occur, rather than preventing unauthorized access upfront. Thus, access control is the most precise category representing the implementation of barriers against unauthorized access.