You are the administrator of the Sybex website. You are working when suddenly web server and network utilization spikes to 100 percent and stays there for several minutes and users start reporting "Server not available" errors. You may have been the victim of what kind of attack?

Denial-of-service attack

Explanation:

Denial-of-service attack -

It is a type of cyber attack , where the hacker can create a machine or any network resource , which is capable to disrupt the server of the host , with the help of the internet , is referred to as the denial of service attack .

The task is accomplished with by flooding the host with many superfluous requests , which can overload the system .

In case of the distributed denial-of-service attack , the flooding is done by many different sources .

Hence , from the given scenario of the question ,

The correct answer is  denial-of-service attack (DoS attack) and distributed denial-of-service attack (DDoS attack) .