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What is a zero-day?
A zero-day is a security flaw that the maker doesn't know about yet, so there is no fix available.
- Category Safety & law
- Also called zero-day exploit
- Updated 20 Oct 2026
Zero-day, explained simply
Zero-day means the maker has had zero days to fix it. Nobody has made a patch.
If attackers find it first, they may use it before anyone can defend. That makes it risky.
You can't fix a zero-day yourself. What you can do is install updates as soon as they arrive and be careful with unknown links.
On ITG Now, our daily AI news stories sometimes mention zero-day flaws when they affect popular tools.
Related terms
VulnerabilityMalwareSupply chain attackRed teamingEncryption
Questions people ask about Zero-day
How can I protect myself from a zero-day?
Keep software updated, use trusted sources and avoid unknown links or files. Updates close the flaw once it is known.
Zero-day vs vulnerability: what is the difference?
A vulnerability is any security flaw. A zero-day is one that the maker doesn't know about yet.
Who finds zero-days?
Security researchers, makers and attackers can all find them. Researchers usually report them so they get fixed.