What is Zero Day? by Ruben Young | Question of the Week | 0 comments Week 2: What is Zero Day? The “Day Zero” or “Zero Day” is the day a new vulnerability is made known. In some cases, a “zero day” exploit is referred to an exploit for which no patch is available yet. (“day one” – day at which the patch is made available). Submit a Comment Cancel replyYou must be logged in to post a comment.