Computer Security Incident
An occurrence that actually or potentially results in adverse consequences to (adverse effects on) (poses a threat to) an information system or the information that the system processes, stores, or transmits and that may require a response action to mitigate the consequences.
Extended Definition: An occurrence that constitutes a violation or imminent threat of violation of security policies, security procedures, or acceptable use policies.
Adapted from: CNSSI 4009, FIPS 200, NIST SP 800-53 Rev 4, ISSG
Source: NICCS™ Portal Cybersecurity Lexicon, National Initiative for Cybersecurity Careers and Studies (https://niccs.us-cert.gov/glossary) as of 11 November 2015, Global Standards