A zero day exploit is a malicious computer attack that takes advantage of a security hole before the vulnerability is known. This means the security issue is made known the same day as the computer attack is released. In other words, the software developer has zero days to prepare for the security breach and must work as quickly as possible to develop a patch or update that fixes the problem.
Zero day exploits may involve viruses, trojan horses, worms or other malicious code that can be run within a software program. While most programs do not allow unauthorized code to be executed, hackers can sometimes create files that will cause a program to perform functions unintended by the developer. Programs like Web browsers and media players are often targeted by hackers because they can receive files from the Internet and have access to system functions.
While most zero day exploits may not cause serious damage to your system, some may be able to corrupt or delete files. Because the security hole is made known the same day the attack is released, zero day exploits are difficult to prevent, even if you have antivirus software installed on your computer. Therefore, it is always good to keep a backup of your data in a safe place so that no hacker attack can cause you to lose your data.