zero-day

adjective

ze·​ro-day ˈzir-(ˌ)ō-ˈdā 

ˈzē-(ˌ)rō-

computing

: of, relating to, or being a vulnerability (as in a computer or computer system) that is discovered and exploited (as by cybercriminals) before it is known to or addressed by the maker or vendor

Thus, in the parlance of the trade, these vulnerabilities are known as "zero-day exploits," because it has been zero days since they have been uncovered and fixed.

—James Bamford

There's a zero-day vulnerability in RealPlayer and Internet Explorer that allows malicious code to be installed …

—Mark Hopkins

… most of what's on the black market doesn't have that zero-day freshness. Criminals typically target older vulnerabilities, for which fixes have already been released …

—Lev Grossman

Examples of zero-day in a Sentence

Recent Examples on the Web

The threat of cyberattack is never far away, be that by Amazon ransomware actors with an impossible-to-recover-from threat, or Windows zero-day exploits and even the hacking of the iPhone USB-C port. —Davey Winder, Forbes, 15 Jan. 2025

This feature expands Bitdefender’s scanning for malicious behaviors, with the aim of detecting zero-day attacks. —PCMAG, 14 Jan. 2025

The worm exploited zero-day vulnerabilities to gain access to Siemens' industrial control systems. —Sam Sabin, Axios, 7 Jan. 2025

Not much is known about the vulnerability itself, as is often the case with such zero-day issues this detail is held back until as many users as possible have had the opportunity to patch against the exploit. —Davey Winder, Forbes, 12 Dec. 2024

Word History

First Known Use

2000, in the meaning defined above