An unintended flaw in software code or a system that leaves it open to the potential for exploitation in the form of unauthorized access or malicious behavior such as viruses, worms, Trojan horses and other forms of malware.
Also referred to as security exploits, security vulnerabilities can result from software bugs, weak passwords or software that s already been infected by a computer virus or script code injection, and these security vulnerabilities require patches, or fixes, in order to prevent the potential for compromised integrity by hackers or malware.
Also see vulnerability scanning and The Difference Between a Virus, Worm and Trojan Horse in the Did You Know? section of Webopedia.