1. A technique to breach the security of a network or information system in violation of security policy.

Source: Explore Terms: A Glossary of Common Cybersecurity Terminology National Initiative for Cybersecurity Careers and Studies (NICCS) https://niccs.us-cert.gov/about-niccs/glossary

2. Software that takes advantage of a vulnerability to undermine a computer’s security .

Source: U.S. Cyberspace Solarium Commission, March 2020, https://subscriber.politicopro.com/f/?id=00000170-c638-d8f7-a7f1-f63b33510000