Attacks and malware
What is Zero-day?
A vulnerability exploited before defenders have had a normal opportunity to patch it.
A zero-day is a vulnerability that attackers exploit before the vendor has released a fix, or before defenders have had a reasonable chance to apply one. The name refers to defenders having had zero days to prepare.
Zero-days are valuable and are often used carefully against selected targets. Once exploitation is discovered and a patch is published, the flaw becomes an n-day, and mass exploitation of unpatched systems often follows quickly.