Page 1473 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

Many forms of malicious code take advantage of zero-day
vulnerabilities, security flaws discovered by hackers that have not

been thoroughly addressed by the security community. There are two
main reasons systems are affected by these vulnerabilities:

The necessary delay between the discovery of a new type of
malicious code and the issuance of patches and antivirus updates.
This is known as the window of vulnerability.

Slowness in applying updates on the part of system administrators

The existence of zero-day vulnerabilities makes it critical that you have

a defense-in-depth approach to cybersecurity that incorporates a
varied set of overlapping security controls. These should include a
strong patch management program, current antivirus software,
configuration management, application control, content filtering, and
other protections. When used in conjunction with each other, these
overlapping controls increase the likelihood that at least one control
will detect and block attempts to install malware.