Zero day or a day zero attack is the term used to describe the threat of an unknown security vulnerability in a computer software or application for which either the patch has not been released or the application developers were unaware of or did not have sufficient time to address.
Since the vulnerability is not known in advance, the exploits often occur without the knowledge of the users. A zero day flaw is considered as an important component when designing an application to be efficient and secure.
Techopedia explains Zero Day Attack
The salient features of the zero day or day zero attacks are:
Zero day attacks usually occur between the time the vulnerability is first found and exploited and the time the application developers releases the necessary solution to counter the exploitation. This timeline is usually termed as the vulnerability window.
Zero day attacks are capable of devastating a network by exploiting the vulnerabilities of the applications involved.
They are not always viruses and can assume other malware forms such as Trojan horses or worms.
For home computer users, the zero day attack is extremely difficult to diagnose as the nature of attack is through a trusted entity.
Update of latest anti-malware software are often recommended, though it can only provide a minimum security against a zero day attack.
Effective methods for protecting against zero day attacks:
Different access controls and restriction including virtual LANs, firewalls can provide protection against zero day attacks.
Single packet authorization can help in providing effective protection in a network with fewer users against zero-day attacks.
Restrict privileges for user accounts. This could mitigate the impact of any possible attacks.