Any kind of malicious activity that attempts to collect, disrupt, deny, degrade, or destroy information system resources or the information itself.
Source(s):
CNSSI 4009-2015
NIST SP 800-12 Rev. 1 under Attack from CNSSI 4009
NIST SP 800-30 Rev. 1 under Attack from CNSSI 4009
NISTIR 8323 under Attack from CNSSI 4009-2015

  An attempt to gain unauthorized access to system services, resources, or information, or an attempt to compromise system integrity, availability, or confidentiality.
Source(s):
NIST SP 800-82 Rev. 2 under Attack from CNSSI 4009

  The realization of some specific threat that impacts the confidentiality, integrity, accountability, or availability of a computational resource.
Source(s):
NIST SP 800-28 Version 2 under Attack

  An unauthorized entity’s attempt to fool a verifier or RP into believing that the unauthorized individual in question is the subscriber.
Source(s):
NIST SP 800-63-3 under Attack

  An attempt by an unauthorized individual to fool a Verifier or a Relying Party into believing that the unauthorized individual in question is the Subscriber.
Source(s):
NIST SP 800-63-2 [Superseded] under Attack