A worm is a type of malware that replicates without any intervention. It jumps from one digital device to another by leaving a copy of itself on anything that connects to the infected system. 

For instance, it can stay on your computer, seemingly harmless, until you plug in a USB stick. That thumb drive will carry a copy of the worm to other computers it’s plugged into. Worms can also end up in a computer through a malware-carrying email attachment or when users access a contaminated website.

Digital worms behave very much like the parasitic worms after which they were named. They live within the bodies of animals. Some of them may transfer into other animals that come in contact with their host. So digital worms spread across computers and devices the same way parasitic worms spread throughout the population.

Other interesting terms…

Read More about a Computer Worm

Computer worms often use areas of an operating system (OS)—the program that lets your system run—where they can remain invisible to the users. Usually, their presence only gets noticed when their continuous replication consumes too many resources, causing a computer to slow down or “hang.”

How does a Computer Worm Work?

Computer worms can infect systems with software vulnerabilities. At times, they are spread as attachments to emails and sent as seemingly harmless files in instant messages. When opened, they instantly infect devices and start spreading.

Some computer worms can change and delete files. Others can cause even more malware to be downloaded onto devices. The additional malware can do anything from exhausting system resources to stealing data and letting a hacker take total control over affected computers.

Types of Computer Worms

There are various types of computer worms, including:

1. Virus-worm hybrids

These spread like normal computer worms but also alter programs like viruses. They are typically used to distribute other viruses or malware.

2. Bot worms

These convert infected computers and any devices connected to them into zombies or bots. They allow hackers to use the botnet—a group of bots—to spread spam or conduct more destructive distributed denial-of-service (DDoS) attacks (when multiple compromised devices or systems attack a single system)

3. IM worms

These spread through different instant messaging (IM) apps and services. They can access contact lists and spread to your contacts’ devices.

4. Email worms

These spread through emails as attachments or downloads from embedded links.

5. Ethical worms

Not all computer worms are harmful, though. These, for instance, were explicitly designed to spread through networks to deliver patches to address security weaknesses.

How to Protect Against Computer Worms

Computer worm infections can be challenging to remedy. But the best antimalware solutions can detect and remove them. So if you believe your computer is infected, run a scan and remove any compromised files. Then prevent them from ever getting into your computer again by setting up a firewall rule that blocks them. Make sure you avoid downloading suspicious files and clicking suspicious links, too, especially if you don’t personally know who sent them.

As a precaution, you should also make sure that your computer systems remain clean. One approach is to run regular system scans with software cleaners that include antimalware functionality. You can check out this link for examples of such tools.

Interesting Facts

Did you know that the Conficker/Downad worm, first seen in 2008, is still active to this day? In its heyday, it successfully infected more than 15 million devices, earning it the reputation of being “one of the most dangerous and sophisticated threats” ever seen. We still see warnings about it from the biggest cybersecurity companies to date. 

Key Takeaways

  • A computer worm is a type of malware that can replicate itself and spread across a network or connected devices without any user intervention after the initial infection.
  • They jump from one device to another by copying themselves onto shared resources, for example, USB drives.
  • Their continuous self-replication often consumes system resources, slowing or crashing the host computer. This is typically the first sign of infection.
  • They can be programmed to perform various malicious actions.
  • Not all worms are malicious. Some, like ethical worms, deliver security patches.

Frequently Asked Questions about Computer Worms

What Is the Difference between a Computer Worm and a Virus?

The main difference is in how they spread. Worms self-replicate and spread independently across a network without having to attach to a host file. Viruses, on the other hand, require a host file, such as an executable program or a macro-enabled document, to execute their code and begin replicating.

How Does a Computer Worm Enter a System?

Common entry points of a worm include the following:

  • Software vulnerabilities: The most dangerous worms use unpatched security flaws in the OS or applications to gain access.
  • Email attachments: They can be sent as innocent-looking attachments or links that install the worm when opened.
  • Instant messages (IM): The worm can access a victim’s contact list and send itself to everyone via chat apps.
  • Removable media: A worm copies itself onto USB drives, infecting new computers when the drives are plugged in.

What Kind of Damage Do Worms Cause?

While a worm’s primary goal is rapid self-replication, its payload can cause severe issues. Its uncontrolled replication consumes huge amounts of CPU, memory, and network bandwidth, and this causes the infected system or even the entire network to slow down or crash. 

Many worms are designed to download and install a second stage of malware, such as ransomware or spyware. They can also be used to turn infected computers into a botnet to launch Distributed Denial-of-Service (DDoS) attacks.

Some worms are used to steal sensitive information or install a backdoor for attackers’ long-term access. 

What Are Some of the Most Famous Computer Worms in History?

Worms have been responsible for some of the most destructive and widespread attacks ever recorded:

  • Morris Worm (1988): Often considered the first major Internet worm, it brought down a significant portion of the early Internet by overloading systems.
  • ILOVEYOU (2000): Spread via an email attachment that looked like a love letter, this worm infected millions of computers globally, clogged email servers, and caused billions of dollars in damage.
  • Code Red (2001): The worm targeted Microsoft web servers and defaced websites with the message “Hacked by Chinese!”
  • Stuxnet (2010): A highly sophisticated worm believed to be an act of cyber warfare, designed to target and cause physical damage to industrial control systems (PLCs).

Sources

  • https://www.dsolutionsgroup.com/top-10-most-dangerous-malware-of-all-time/
  • https://www.ibm.com/think/topics/ddos
  • https://www.giac.org/paper/gsec/1000/code-red-dew/101919
  • https://edition.cnn.com/2020/05/01/tech/iloveyou-virus-computer-security-intl-hnk
  • https://alumni.cornell.edu/cornellians/morris-worm/
  • https://spectrum.ieee.org/the-real-story-of-stuxnet