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
Instead of just one operating system being compromised, the series imagines a sophisticated attack exploiting multiple zero-day vulnerabilities simultaneously.
—Gordon G. Chang, Newsweek, 4 Mar. 2025
The latter played a huge hand in the collapse of the stock Thursday, a day after the company reported earnings , because once the stock crested and started going down the zero-day options act like gasoline thrown on a slow-burning fire.
—Jim Cramer, CNBC, 2 Mar. 2025
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
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Gordon G. Chang, Newsweek, 4 Mar. 2025
The latter played a huge hand in the collapse of the stock Thursday, a day after the company reported earnings , because once the stock crested and started going down the zero-day options act like gasoline thrown on a slow-burning fire.
—Jim Cramer, CNBC, 2 Mar. 2025
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
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 12 Mar. 2025.
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