A possible danger that might exploit a vulnerability, a is a potential for violation of security which exists when there is a circumstance, capability, action, or event that could breach security and cause harm.

Answer is: A THREAT

Explanation:

In computer security, a threat is a possible danger that may exploit a vulnerable to breach a security and therefore cause possible harm.

A threat can either be intentional (I.e. Hacking: an individual cracker or organization) or accidental ( e.g. malfunctioning of a computer) or otherwise a circumstance, action or event.

A threat is a potential for violation of security, which exists when there is a cicumstance, capability, event or action that could breach security and cause harm. That is, a threat is a possible danger enabling exploitation of a vulnerability.

Therefore the answer that best suits the question is A THREAT.