Cybersecurity Glossary
Zero Day
A vulnerability being exploited before the vendor has released a fix.
What Zero Day means
A zero day is a flaw for which no patch yet exists, so defenders have had zero days to prepare. Once the vendor publishes a fix, the clock starts on a different race, because attackers study patches to work out what to exploit on systems that have not updated yet.
Why Zero Day matters for small businesses and nonprofits
Zero days get attention, but for a small organisation the far bigger risk is the known vulnerability left unpatched for months. Most incidents involve flaws with fixes that were available long before the attack.
What to do about Zero Day
- Patch quickly, because the window after a fix is published is when mass exploitation happens
- Subscribe to advisories for the few products you truly depend on
- Use layered defences so a single unpatched flaw is not sufficient on its own
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