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
Human expertise is critical for investigating zero-day attacks, creative problem-solving and post-incident analysis to improve defenses.
—Mala Ramakrishnan, Forbes.com, 15 May 2025
Options and zero-day options have become a significant part of the daily trading landscape in the last several years.
—Jason Gewirtz, CNBC, 10 May 2025
Clop exploited a zero-day vulnerability in Cleo’s enterprise file transfer software, technology used by many large organizations to securely transmit sensitive business data.
—Kurt Knutsson, FOXNews.com, 25 Apr. 2025
The zero-day vulnerabilities were found before developers were made aware and could patch them.
—Kate O'Flaherty, Forbes.com, 17 Apr. 2025
See All Example Sentences for zero-day
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Mala Ramakrishnan, Forbes.com, 15 May 2025
Options and zero-day options have become a significant part of the daily trading landscape in the last several years.
—Jason Gewirtz, CNBC, 10 May 2025
Clop exploited a zero-day vulnerability in Cleo’s enterprise file transfer software, technology used by many large organizations to securely transmit sensitive business data.
—Kurt Knutsson, FOXNews.com, 25 Apr. 2025
The zero-day vulnerabilities were found before developers were made aware and could patch them.
—Kate O'Flaherty, Forbes.com, 17 Apr. 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 21 May. 2025.
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