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1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minuteA computer worm is standalone malware that can make copies of itself and spread between computers or systems, often over a network. Unlike a conventional virus, it does not need to attach itself to another program to run. A worm may consume system resources or deliver other harmful functions.
What makes malware a computer worm?
The defining feature is independent replication: a worm can run as a program in its own right and propagate a working copy to another system. NIST’s glossary describes worms as self-contained programs that spread through data-processing systems or networks; one definition specifies that replication can occur without a host program or user intervention.
That describes the malware’s propagation mechanism, not everything it may do. A worm can mainly burden systems as it spreads, or its activity can be combined with another malicious function.
How is a worm different from a virus?
| Feature | Worm | Conventional virus |
|---|---|---|
| Needs another program to host it | No; it is self-contained. | Yes; it inserts itself into another program. |
| How it becomes active | Can run independently. | The host program must run for the virus to become active. |
| How it propagates | Can copy a working version to another system, often through a network. | Propagates by inserting itself into a host program. |
These labels describe mechanisms, and they are not mutually exclusive. Blended malware can combine methods; for example, CISA describes WannaCry as ransomware containing a worm. CISA’s WannaCry advisory recommends isolating affected systems to limit further spread.
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How do computer worms spread?
The route depends on the particular worm and the systems it can reach. A network-service worm may exploit a vulnerability in an operating system or application service to reach other computers. Worms can also use network mechanisms to propagate; there is no single route used by every worm.
Because a worm can replicate without attaching to a program, its spread does not necessarily depend on someone opening an infected document or application. The precise behavior varies, so the label “worm” alone does not identify the vulnerability, affected systems, or other functions involved.
What damage can a worm cause?
Replication can consume processing time and storage, slowing systems or disrupting their availability. Malware may also affect confidentiality or integrity, and a worm can carry or be combined with additional malicious behavior. The impact therefore depends on both how it spreads and what it does after reaching a system.
How can you reduce the risk of a worm infection?
Layered defenses reduce opportunities for malware to run and spread, but no single measure guarantees protection. CISA-hosted federal guidance recommends:
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- Install operating system and application security updates promptly.
- Keep antivirus or antimalware software updated.
- Scan downloaded software before running it, and avoid executing downloads you do not trust.
- Restrict software installation privileges to people and accounts that need them.
What should you do if you suspect a worm infection?
For an organization, use its incident-response plan and alert the information security team. CISA-hosted guidance titled Current Malware Threats and Mitigation Strategies dates its operational recommendations to May 2005, so treat its checklist as legacy guidance rather than current policy. It recommends promptly disconnecting a small number of infected systems, applying appropriate patches, cleaning with antivirus signatures verified for the specific variant, notifying security staff, and monitoring for reinfection. Current procedures should be verified against the organization’s response plan and qualified incident-response advice.
Containment and recovery depend on the infection and network. Avoid assuming that removing one visible symptom has stopped propagation; organizations should monitor affected systems and segments for signs of reinfection.
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