An occurrence that results in actual or potential jeopardy to the confidentiality, integrity, or availability of an information system or the information the system processes, stores, or transmits or that constitutes a violation or imminent threat of violation of security policies, security procedures, or acceptable use policies. See cyber incident. See also event, security-relevant, and intrusion.
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CNSSI 4009-2015 under incident from FIPS 200 - Adapted

  Anomalous or unexpected event, set of events, condition, or situation at any time during the life cycle of a project, product, service, or system.
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NIST SP 800-160v1r1 under incident from ISO/IEC/IEEE 15288:2015

  An occurrence that actually or imminently jeopardizes, without lawful authority, the confidentiality, integrity, or availability of information or an information system; or constitutes a violation or imminent threat of violation of law, security policies, security procedures, or acceptable use policies.
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NIST SP 800-171r3 under incident from 44 U.S.C., Sec. 3552
NIST SP 800-172 under incident from 44 U.S.C., Sec. 3552
NIST SP 800-172A under incident from 44 U.S.C., Sec. 3552
NIST SP 800-37 Rev. 2 under incident from 44 U.S.C., Sec. 3552
NIST SP 800-53 Rev. 5 under incident from PL 113-283 (FISMA)

  An occurrence that actually or potentially jeopardizes, without lawful authority, the confidentiality, integrity, or availability of information or an information system; or constitutes a violation or imminent threat of violation of security policies, security procedures, or acceptable use policies.
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NIST SP 800-128 under incident from 44 U.S.C., Sec. 3552

  An occurrence that actually or imminently jeopardizes, without lawful authority, the integrity, confidentiality, or availability of information or an information system; or constitutes a violation or imminent threat of violation of law, security policies, security procedures, or acceptable use policies.
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NIST SP 800-61r3 under cybersecurity incident from PL 113-283 (FISMA)

  A cybersecurity event that has been determined to have an impact on the organization prompting the need for response and recovery.
Sources:
NIST Cybersecurity Framework Version 1.1
NIST Privacy Framework Version 1.0 from NIST Cybersecurity Framework Version 1.1

  An occurrence that (1) actually or imminently jeopardizes, without lawful authority, the integrity, confidentiality, or availability of information or an information system; or (2) constitutes a violation or imminent threat of violation of law, security policies, security procedures, or acceptable use policies.
Sources:
NIST Privacy Framework Version 1.0 from OMB M-17-12