Which type of cyber attack primarily affects availability of services?

The type of cyber attack that primarily affects the availability of services is a Denial of Service (DoS) attack. A DoS attack is designed to make a service unavailable to its intended users by overwhelming it with a flood of illegitimate requests or traffic. This can result in legitimate users being unable to access the service, fulfilling the attacker's goal of disrupting operations.

In contrast, phishing is primarily a method to capture sensitive information by masquerading as a trustworthy entity, while malware encompasses a broader category of malicious software that can affect confidentiality and integrity rather than just availability. A data breach, although it may impact availability indirectly, is primarily concerned with unauthorized access to confidential information. Hence, the DoS attack is the most direct method for compromising service availability.