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
James BamfordThere's a zero-day vulnerability in RealPlayer and Internet Explorer that allows malicious code to be installed …—Mark Hopkins
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
Lev GrossmanExamples of zero-day in a Sentence
Recent Examples on the Web
With Samsung Galaxy owners still awaiting Android 15 and the latest Android zero-day fix, both of which Pixels received right away, something needs to change.
—Zak Doffman, Forbes, 19 Feb. 2025
If a zero-day virus or data-stealing Trojan gets past your defenses, an antivirus update will typically remove it before long.
—PCMAG, 9 Feb. 2025
These hackers gather to see who can be the first, running against the clock, to successfully hack a variety of targets from smartphones to printers and routers using a zero-day compromise.
—Davey Winder, Forbes, 23 Jan. 2025
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
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Zak Doffman, Forbes, 19 Feb. 2025
If a zero-day virus or data-stealing Trojan gets past your defenses, an antivirus update will typically remove it before long.
—PCMAG, 9 Feb. 2025
These hackers gather to see who can be the first, running against the clock, to successfully hack a variety of targets from smartphones to printers and routers using a zero-day compromise.
—Davey Winder, Forbes, 23 Jan. 2025
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
See All Example Sentences for zero-day
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Cite this Entry
“Zero-day.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/zero-day. Accessed 5 Mar. 2025.
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