What defines a Zero Day Attack?

A Zero Day Attack is characterized by the exploitation of a vulnerability in software or hardware that is unknown to the vendor and, crucially, for which no patch or defense has been made available. This means that the attacker takes advantage of the vulnerability before the developers have had the opportunity to fix the flaw, rendering standard protective measures ineffective.

The term "zero day" refers specifically to the fact that at the time the attack occurs, there have been zero days of protection against the exploit. This makes such attacks particularly dangerous as they can be carried out without any prior warning or the possibility of mitigation by the software's creators or users.

In contrast, the other options describe scenarios that do not align with the essence of a Zero Day Attack. A patch being released indicates that the vulnerability is known and has been addressed, while a public disclosure without exploitation or the identification and blocking of a threat actor involves a response to threats rather than the exploitation of unknown vulnerabilities.