A zero-day vulnerability is a computer-software vulnerability that is unknown to those who would be interested in mitigating the vulnerability. Until the vulnerability is mitigated, hackers can exploit it to adversely affect computer programs, data, additional computers or a network. An exploit directed at a zero-day vulnerability is called a zero-day exploit, or zero-day attack. In the jargon of computer security, Day Zero is the day on which the interested party learns of the vulnerability.