CyberGuard dictionary / Malware
Trojan Horse
A Trojan horse is software that appears legitimate or desirable but performs an undisclosed malicious action when used.
In simple terms
A Trojan relies on deception rather than self-replication; the user thinks they are installing or opening something useful.
Technical explanation
Trojanized installers, documents, or packages can execute a hidden payload alongside their expected behavior. A Trojan may later download other malware, steal data, or provide remote access, but those actions are separate capabilities.
The program gains execution by appearing useful or legitimate; it does not need to replicate to be a Trojan. Signing, provenance checks, and controlled installation reduce exposure but must be interpreted carefully.
Examples in practice
A fake utility installs its advertised screen tool while quietly creating an unauthorized remote-access service.
A fake PDF utility opens documents as promised while quietly installing a remote-access component. The user notices unexpected startup behavior, and IT traces it to the download.
Why it matters
Checking software origin and integrity helps avoid trusting a malicious package because its interface looks normal.
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Sources and further reading
Published 2026-10-15 · Last updated 2026-10-15 · CyberGuard editorial content. Source links provide context; they do not imply endorsement.