Answer:
Zero day
Explanation:
Zero day attack is the term used to describe the threat of an unknown security vulnerability in a computer software or application for which either the patch has not been released or the application developers were unaware of or did not have sufficient time to address.
Since the vulnerability is not known in advance, the exploits often occur without the knowledge of the users. A zero day flaw is considered as an important component when designing an application to be efficient and secure.