Answer:
C. Zero-day attack.
Step-by-step explanation:
A zero-day attack is a type of cyber attack that exploits a vulnerability in software or hardware that is unknown to the party responsible for patching or otherwise protecting the affected system. These attacks can have a significant impact because they take advantage of vulnerabilities that have not yet been discovered or fixed. The term "zero-day" refers to the fact that the attacker is able to take advantage of the vulnerability on the same day that it is discovered, before the vendor has had a chance to develop and distribute a patch to address the issue.