Precursor Posted on December 24, 2019December 24, 2019 by Ty Mezquita Image Source A precursor is an observable occurrence or sign that an attacker may be preparing to cause an incident. Related Term: Indicator Source: CNSSI 4009, NIST SP 800-61 Rev 2 Share this on your social networks. Help Friends, Family, and Colleagues become more aware and secure.