After a security issue with website access, what attack most likely occurred on the original DNS server?

The context of this question revolves around vulnerability in the DNS server that impacts website access. The best option that aligns with the described scenario is DNS cache poisoning.

When a DNS cache is poisoned, the DNS server caches fraudulent entries, allowing an attacker to redirect traffic from a legitimate site to a malicious one. When users attempt to access the original website, they are unknowingly sent to a different, potentially harmful location, which aligns with the issue of compromised access.

This attack exploits the way DNS servers temporarily store resolved entries to enhance efficiency. If an attacker can supply false information to the server, it can create a situation where users encounter incorrect or dangerous sites without their knowledge, leading to the described “security issue with website access.”

In contrast, options like domain hijacking involve taking control of a domain name itself, which does not directly affect DNS server functionality. A distributed denial-of-service attack targets the availability of services but does not alter DNS records. Lastly, DNS tunneling is a technique used to encapsulate data within DNS queries but isn't directly related to impairing access due to compromised DNS entries. Thus, the focus on the alteration of DNS cache entries makes DNS cache poisoning the most appropriate answer.