What type of cybersecurity breach renders a computer or online service unavailable to users?

A denial-of-service (DDoS) attack is specifically designed to make a computer, network, or online service unavailable to its intended users. This is achieved by overwhelming the target with a flood of traffic, often from a network of compromised computers known as a botnet.

The primary goal of a DDoS attack is disruption, such that legitimate users cannot access the services they need. Unlike other types of cybersecurity breaches, such as ransomware or data breaches, which may focus on data theft or encryption, DDoS attacks are all about incapacitating the service itself.

Phishing attacks are primarily about tricking users into providing sensitive information; ransomware attacks involve locking files and demanding payment for access; and data breaches involve unauthorized access to confidential data. Therefore, DDoS attacks stand out as the type of cybersecurity breach that directly impacts service availability.