CyberGuard dictionary / Malware
Fileless Malware
Fileless malware is malicious activity that relies heavily on memory and legitimate system tools instead of a conventional standalone malicious file on disk.
In simple terms
An attacker can misuse tools already installed on a computer, leaving fewer obvious files to scan.
Technical explanation
Scripts, injected code, scheduled tasks, and trusted administrative utilities may be used to execute payloads or maintain access. The term does not mean no file ever exists; detection often depends on behavior, process ancestry, and logs.
The label describes techniques that rely heavily on memory, scripts, or legitimate system tools rather than a conventional malicious file on disk. Logs and behavior remain important because absence of a file is not absence of compromise.
Examples in practice
A compromised account launches a built-in scripting tool to download and run code in memory rather than saving a normal executable.
A malicious command runs through an approved scripting interpreter and creates a scheduled task. Endpoint telemetry and task history reveal the activity even though no standalone executable is found.
Why it matters
File-focused scanning alone may miss activity carried through legitimate tools and memory.
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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.