What aspect of computer security ensures resources are available when needed?

The aspect of computer security that ensures resources are available when needed is availability. Availability refers to the ability of a system or resource to remain accessible and operational for users when required. This concept is critical in information security because, without availability, even the most secure and confidential data becomes useless if it cannot be accessed by authorized users in a timely manner.

In practical terms, availability focuses on factors such as system uptime, redundancy, resilience against attacks (like Denial of Service attacks), and proper disaster recovery measures. Ensuring availability means implementing strategies to avoid outages, such as load balancing, backups, and failover systems that help maintain continuous access to data and services.

In contrast, integrity concerns the accuracy and trustworthiness of data, ensuring that information remains unaltered and authentic over time, while confidentiality deals with protecting information from unauthorized access. Reliability, though closely related, emphasizes the quality and consistency of the services provided rather than the assurance of access. Thus, among the provided options, availability is the best fit for ensuring resources are accessible when users need them.