A Zero-Day Attack, also known as a zero-day exploit or zero-hour attack. It occurs when hackers exploit a vulnerability in hardware or software or firmware that is unknown to the vendor. An attacker discovers the vulnerability, swiftly creates an exploit, and uses it to launch an attack, before a patch is available. Zero-day attacks are severe security threats with high success rates as businesses do not have defenses in place to detect or prevent them. These attacks can be viruses or malware such as worms or Trojans.

Signature-based security solutions can’t detect a zero-day attack, the reason being until the software vulnerability is publicly known, the security solutions may not have a way to detect it. You need to react to a zero-day attack quickly to prevent widespread damage to the network or data theft.

A few best practices to Mitigate Zero-Day Attacks. 

• Educate users: It is good to train all your organization employees in basic threat mitigation, such as how to respond appropriately to unknown email attachments or apparent anomalous activity. Email attachments are a common threat vector for zero-day attacks. Email attachments can exploit vulnerabilities in specific file types and web applications.
  

• Use intrusion prevention systems (IPS): Look for an IPS that has network protection offering content validation and forensics, application integrity checking, third-party verification, and much more. IPsec encrypts and authenticates all network traffic, allowing a system to rapidly identify and isolate non-network traffic and suspicious activity. With this information, organizations stand a better chance of being able to recognize and stop attacks before damage is done.
  

• Deploy a web application firewall: Will help your organization react to threats in real-time. A web application firewall continually scans incoming data for threats, providing organizations with the information necessary to suppress suspicious activity and stop an impending attack from occurring.