DEFINITION

• A type of standalone malware that replicates itself to spread across computers and networks without needing to attach to a host file or be manually executed. 

• Unlike viruses (101), worms are fully autonomous and often exploit system vulnerabilities or misconfigurations to move laterally, causing rapid infection across environments. 

DAMAGE

• Consumes bandwidth and system resources, potentially leading to network outages

• Can carry destructive payloads like ransomware, spyware, or backdoors

• May disable security software or alter system settings to persist

• Can result in mass data loss, service downtime, and security breaches

Examples/Usage

• WannaCry: Spread globally using an SMB vulnerability (EternalBlue), encrypting data and demanding ransom.

• SQL Slammer: Crippled networks by exploiting a buffer overflow in Microsoft SQL Server.

• Conficker: Infected millions by exploiting Windows vulnerabilities and weak passwords.

• Example usage in a report: "Systems were compromised via a worm that propagated internally through unpatched SMB services."

Remediation

• Immediately disconnect infected machines from the network.

• Apply relevant patches and security updates (e.g., disable SMBv1).

• Perform thorough scans using up-to-date antivirus or EDR tools.

• Audit network for lateral movement and potential backdoors.

• Implement segmentation and least privilege access policies.

Good to Know

• Worms don’t require user action — they often spread silently and quickly.

• Many modern worms operate in-memory, making detection harder.

• They're often used as delivery mechanisms for more dangerous threats.

• Network traffic anomalies are a common early indicator of a worm infection.