A zero-day (also known as zero-hour or 0-day or ... - dofaq.co
zero day (computing)

A zero-day (also known as zero-hour or 0-day or ...

wikipedia - 26 Aug 2015
A zero-day (also known as zero-hour or 0-day or day zero) vulnerability is an undisclosed computer-software vulnerability that hackers can exploit to adversely affect computer programs, data, additional computers or a network. It is known as a "zero-day" because it is not publicly reported or announced before becoming active, leaving the software's author with zero days in which to create patches or advise workarounds to mitigate its actions.

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