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
All those users must now update Chrome, after Google warned that a new zero-day exploit has been found in the wild.
—Zak Doffman, Forbes.com, 28 Mar. 2025
Homeland tackled national and global cyberterrorism, including the hacking of elections, but the series never encountered a zero-day attack.
—Jackie Strause, HollywoodReporter, 27 Mar. 2025
The zero-day vulnerability, dubbed CVE-2025-2783, created an attack that could infect a Windows PC if the user clicked on a malicious link, according to antivirus provider Kaspersky, which discovered the threat.
—Michael Kan, PC Magazine, 26 Mar. 2025
This follows Google’s warning early this month that two zero-day vulnerabilities are being actively exploited in the wild.
—Zak Doffman, Forbes, 23 Mar. 2025
See All Example Sentences for zero-day
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Zak Doffman, Forbes.com, 28 Mar. 2025
Homeland tackled national and global cyberterrorism, including the hacking of elections, but the series never encountered a zero-day attack.
—Jackie Strause, HollywoodReporter, 27 Mar. 2025
The zero-day vulnerability, dubbed CVE-2025-2783, created an attack that could infect a Windows PC if the user clicked on a malicious link, according to antivirus provider Kaspersky, which discovered the threat.
—Michael Kan, PC Magazine, 26 Mar. 2025
This follows Google’s warning early this month that two zero-day vulnerabilities are being actively exploited in the wild.
—Zak Doffman, Forbes, 23 Mar. 2025
See All Example Sentences for zero-day
Cite this Entry
“Zero-day.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/zero-day. Accessed 3 Apr. 2025.
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