1. A computer program that appears to have a useful function, but also has a hidden and potentially malicious function that evades security mechanisms, sometimes by exploiting legitimate authorizations of a system entity that invokes the program.
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; The State and Local Election Cybersecurity Playbook, Defending Digital Democracy Project, Harvard Kennedy School Belfer Center for Science and International Affairs, https://www.belfercenter.org/sites/default/files/files/publication/StateLocalPlaybook%201.1.pdf
2. A computer program that appears to have a useful function, but also has a hidden and potentially malicious function that evades security mechanisms, sometimes by exploiting legitimate authorizations of a system entity that invokes the program.
Source: U.S. Cyberspace Solarium Commission, March 2020, https://subscriber.politicopro.com/f/?id=00000170-c638-d8f7-a7f1-f63b33510000
3. Program containing hidden code allowing the unauthorized collection, falsification, or destruction of information. (CNSS Instruction No. 4009).
4. A computer program with an apparently or actually useful function that contains additional (hidden) functions that surreptitiously exploit the legitimate authorizations of the invoking process to the detriment of security (for example, making a “blind copy” of a sensitive file for the creator of the Trojan horse). (DoD 5220.22.22-M-Sup 1, NISPOM Supplement, Feb 1995).
5. A malicious program that pretends to be a benign application; it purposefully does something the user does not expect. Trojans are not viruses since they do not replicate, but they can be just as destructive. (McAfee.com, accessed 15 Nov 2010).
Source: Terms & Definitions of Interest for DoD Counterintelligence Professionals Office of the National Counterintelligence https://www.dni.gov/files/NCSC/documents/ci/CI_Glossary.pdf
6. Trojan horses (often referred to as Trojans) are programs that covertly perform harmful actions while disguised as a useful application or file.
Source: Information Assurance Situation in Switzerland and Internationally, Reporting and Analysis Centre for Information Assurance MELANI https://www.newsd.admin.ch/newsd/message/attachments/11945.pdf