What is a zero-day exploit?

A zero-day exploit refers to a cyberattack that takes place on the same day a vulnerability is discovered and before any patches or fixes have been released to address that vulnerability. The term "zero-day" indicates that the software developer has had zero days to address the security flaw, leaving systems exposed and vulnerable to exploitation.

This is particularly dangerous because once a vulnerability is identified, attackers can quickly create an exploit to take advantage of it, often targeting systems that have not yet received the necessary updates. By attacking at this stage, cybercriminals can gain unauthorized access, steal data, or cause significant disruption.

The other options do not align with the definition of a zero-day exploit. Attacks that happen after a patch is released deal with vulnerabilities that have already been addressed, while targeting outdated software applies to systems that may or may not have had vulnerabilities discovered. Lastly, the idea of any attack not detected by security systems pertains to detection capabilities rather than the specific timing and circumstances surrounding the exploitation of a vulnerability.