ISC Malware · Updated November 2026
Virus, Worm, Trojan, Ransomware: How Does the Malware Behave?
Classify malware by how it spreads, disguises itself, or harms the victim.
Virus
Typically attaches to a host file or program and spreads when that host executes or is shared.
Worm
Can self-propagate across systems or networks without requiring the same host-file behavior as a virus.
Trojan
Pretends to be legitimate software or content while performing malicious activity.
Ransomware
Restricts access to systems or data, often through encryption, and demands payment or another concession. Multiple malware techniques can overlap in one campaign.
The takeaway
Virus attaches. Worm spreads. Trojan disguises. Ransomware denies access for extortion.
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FAQ
Can a worm spread without opening every infected file?
Yes.
Does ransomware always arrive through phishing?
No.
Can one attack use multiple malware techniques?
Yes.