What Is a Zero-day Attack?
What is a Zero-Day Vulnerability or Exploit?
A zero-day (or 0-day) vulnerability is a security risk in a piece of software that is not publicly known about and the vendor is not aware of. A zero-day exploit is the method an attacker uses to access the vulnerable system. These are severe security threats with high success rates as businesses do not have defenses in place to detect or prevent them.
A zero-day attack is so-called because it occurs before the target is aware that the vulnerability exists. The attacker releases malware before the developer or vendor has had the opportunity to create a patch to fix the vulnerability.
The term "zero day" comes from the world of pirated digital media. A pirated version of a movie, music, or software is referred to as "zero day" when it becomes available at the same time or before the official release. In other words, the pirated version is published zero days after the official version.