[(What is zero-day attack?)]

♦The zero-day attack is the exploitation of unpatched software vulnerabilities.It is also known as a zero hour attack, takes advantage of computer vulnerabilities that do not currently have a solution.Typically, a software company will discover a bug or problem with a piece of software after it has been released and will offer a patch another piece of software meant to fix the original issue. A zero day attack will take advantage of that problem before a patch has been created.
It is named zero day because it occurs before the first day the vulnerability is known.