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Computer Worms: How Do They Work and How to Prevent it?

21st Sep, 2023
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    Computer Worms: How Do They Work and How to Prevent it?

    Computer Worms are a collection of codes used by a malicious user to gain unauthorized access to a computer system. It can be used by the administrator of the infected computer to gather sensitive information related to the organization or as a warfare weapon against an organization. With the growing trend in cybersecurity and ethical hacking, if you want to get a hand on ethical hacking, do checkout Ethical Hacking Training. 

    Computer worms have been a growing threat over the last decade, and their destructive potential continues to grow in geometrical progression. More and more software companies are now incorporating countermeasures against computer worm attacks into their products. Several governments are also starting to take measures. There are still ways to get infected with a computer worm, but the good news is that there are also ways to prevent it. Your best defense is always to have an updated anti-virus program and keep your firewalls up to date. These can identify and help prevent any computer worms that have infiltrated your system.

    Computer Worm Overview

    An upcoming new topic in the IT sector is computer worm attacks, which are considered to enter the invasion and propagation phases at intervals of a few hours. Since worms are designed to be spread by reproducing themselves, they can cause several problems, depending on how the worm operates. Infected computers can become a member of a botnet, meaning that the attacker controls all their resources for any purpose. Most notably, it enables sending out more and more viruses over the network, thus creating attacks called DDoS (Direct Denial of Service) attacks. The damage from such an attack is not limited by the number of infected machines alone but also depends on how much power these computers have and what they perform.  

    The increasing need for networking among computer systems is a fact of the present age. In this age, it becomes increasingly important to protect connected computers from unrelenting attacks by malicious computer programs called computer worms. 

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    Computer Worm Definition

    A computer worm is described as a standalone malware computer program that attacks computers autonomously or spreads itself over a computer network. Unlike viruses, worms do not need to attach themselves to other programs to spread. A worm is a type of malicious software designed to spread copies of itself across networks by exploiting security vulnerabilities. 

    A Computer worm is also a kind of malware. They are typically used to perform malicious activities. So, what is its most distinctive component? Its capacity to spread quickly without including people. Since it self-reproduces once inside one's computer, cell phone, or tablet, it's possibly the most-risky malware.  

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    Types of Computer Worms

    There are several types of malicious computer worms, lets checkout the important ones here 

    1. Email Worms

    Email worms replicate themselves by generating new messages and sending them out to all the addresses that are stored in a user's contact list. Successful email worms often use social engineering and phishing methods to entice users to click the attached file. The mails include a malicious executable file that infects the new machine when the receiver downloads the attachment. 

    2. File-sharing Worms

    Worms that propagate via file sharing do so by duplicating their files in shared folders and then spreading across peer-to-peer networks. The harmful programmes that are used to spread worms are often disguised as data files by their creators.

    3. Crypto Worms

    Crypto worms encrypt the data on the victim's system. Perpetrators/hackers can use this type of worm in ransomware attacks, where they follow up with the victim and demand payment in exchange for a key to decrypt the files.

    4. Internet Worms

    There is a certain group of computer worms that specifically target popular websites with poor security. If they can infect the site, they can infect a computer accessing the site.

    5. Instant Messaging Worms

    In the same way, as email worms manipulate the system, instant messaging worms hide behind attachments or links, which the worm then uses to continue to disseminate itself to the contact list of the person who was infected. The only notable difference is that rather than appearing in an email, it arrives in the form of an instant message on a chat site.

    How Does a Computer Worm Spread?

    Computer Worms get transmitted either through software vulnerabilities or could arrive as attachments in spam emails or instant messages (IMs) or files downloaded from open internet or opening spam links. Computer worms are spread mainly via social engineering and phishing 

    Social engineering—the act of tricking people into doing something they wouldn't do otherwise—can be used to spread worms across networks.  Worms can be distributed via email, P2P file sharing and targeted phishing attempts.  Some worms can self-replicate on networks by spreading through shared access points.   Security holes in software can be exploited by worms as well.  Computer Worms can infect systems via third-party devices like USB sticks and external hard drives. Social engineering is gaining personal information by exploiting a person's trust in others. A fraudulent email can carry worms in an attachment that users could click on or visit websites designed to infect their systems with Computer worms.

    1. Phishing

    Phishing is a type of cyber-attack that involves tricking users into clicking on malicious links or visiting websites designed to infect them with malware. Instances of social-engineering attacks are becoming more common as people interact more frequently via instant messaging (IM) platforms like Internet Relay Chat (IRC).

    2. Spear-Phishing

    Spear Phishing scams conducted by email or other forms of electronic communication that are directed against a particular person, organization, or company are known as spear phishing. Although the intention is often to steal data for nefarious reasons, hackers may also have the intention of installing malware on the computer of the victim they are targeting. 

    3. Networks

    Networks can be infiltrated by worms via shared access, security holes in programs that are exploited by worm variants and file sharing. Computer Worms can spread across networks by exploiting software vulnerabilities, but they also may be manually installed by someone who has gained access to your computer. When a worm spreads across networks, it can affect every device connected to that network. 

    4. Security Holes

    Exploiting software vulnerabilities is a method that some worm versions use to gain access to a computer system. 

    5. File Sharing

    Computer worms that spread via file sharing will duplicate themselves and store them in a shared folder before sending it out across a peer-to-peer network. 

    6. Social Networks

    Worms have caused issues on several social networking sites, including MySpace, which hosts user content.  

    7. Instant Messengers (IMs)

    Text messages and instant messaging services, such as Internet Relay Chat, are prime vectors for the transmission of all kinds of malicious software, including worms (IRC). 

    8. External Devices

    Worms have the ability to infect external hard drives and USB sticks.

    What Does a Computer Worm Do?

    Computer worms can obliterate your system in an assortment of ways. Some imitate themselves to the place where they consume all suitable extra room and framework memory, delivering your gadget unusable. Others adjust or eliminate records and even introduce vindictive programming. 

    Worms may change or remove data on a computer, and some even can inject extra harmful code into the system. Sometimes the only thing a computer worm wants to do is produce copies of itself repeatedly, which may deplete system resources like the amount of space on the hard drive or the bandwidth available to the system by overloading the network. Worms, in addition to wreaking havoc on the resources of a computer, may also steal data, install a backdoor, and enable a hacker to take control over a computer and its system settings. Worms can also install a backdoor on a computer.

    Computer Worm Examples

    There have been many tremendous computer worm attacks in the past, and the worst thing is, they exist till date. The famous MyDoom worm, for instance, is still actively breathing and sends through email attachments 16 years after its creation. 

    1. Blaster

    When the Blaster was first used, it would show two messages when the programme was run: "I simply want to say LOVE YOU SAN" and "billy gates why do you make this possible? Put an end to earning money and repair your programme immediately!!” Nevertheless, it resulted in the forced shutdown of computers. 

    2. Sobig Worm

    The Sobig worm existed in a number of different iterations, ranging from Sobig. A through Sobig.F. It was sent as an attachment to emails with generic subject lines such as "Thank You" or "Re: Details." The computer worm, after it has infected a computer, will then spread to additional contacts that the user has in their address book. 

    3. BlackBox Worm

    The BlackBox worm was a form of computer virus that ate up all of the available resources on the machine. Any software that was being executed on Friday the 13th of any year, was removed when it was activated. It also continually infected.exe files until they were too huge for the machine to handle, at which point it deleted them. 

    4. Morris Worm

    The Morris worm was the first computer worm discovered with real-world impact. A computer science student accidentally created the worm in 1988, which crashed many computers which it affected. 

    5. My DOOM

    Mydoom, the most destructive computer virus epidemic in history, was estimated to have caused damages in the amount of $38 billion in 2004, but its true cost, when adjusted for inflation, was $52.2 billion. This piece of malware, which is officially a "worm" and is also known as Novarg, spreads itself by mass emailing. At one point in time, the Mydoom virus was accountable for twenty-five percent of all emails that were sent. Mydoom gathered email addresses from infected computers and used them to distribute copies of itself to other computers. In addition, it connected all the infected workstations together into a network of computers known as a botnet, which was used to launch distributed denial of service assaults. These assaults have the purpose of bringing an intended website or server to its knees. The creator of this malicious computer worm was never identified, despite the fact that a reward of two hundred and fifty thousand dollars had been offered. 

    6. Nimda

    Nimda was the first computer worm that modified existing websites to offer malicious downloads.4 It spread by sending mass emails and then began propagating in LANs. 

    7. Code Red

    The Code Red worm initiated a DDoS attack (distributed denial of service) aimed at the U.S. White House using infected computers. This attack forced the White House and its web servers to change IP addresses. 

    8. I LOVE YOU

    The year 2000’s ILOVEYOU virus worked by sending a bogus “love letter” that looked like a harmless text file. Like Mydoom, this attacker sent copies of itself to every email address in the infected machine’s contact list. As soon as it was released on May 4, it had already spread to more than 10 million personal computers. The virus was created by a college student in the Philippines named Onel de Guzman. Because he was short on cash, he decided to write a virus that would steal users' credentials and allow them to access paid web services for free. He reportedly had no idea how far his creation would spread. The name "Loveletter" has also been given to this virus. 

    9. Ryuk

    Although Ryuk wasn't always a worm, it's now worm-like ransomware

    10. SQL Slammer

    Infamy was brought upon the SQL Slammer worm by the fact that it slowed down the flow of Internet traffic by launching denial-of-service attacks on specific Internet servers. 

    11. Conflicker

    Conficker is a virus that was identified in 2009 that is still actively infecting a huge number of legacy systems and has the potential to do a significant amount of damage in the event that it ever becomes operational. 

    12. Storm Worm

    Storm Worm, used social engineering by spreading bogus reports of a catastrophic storm in order to install botnets on computers that had already been infected. 

    13. Stuxnet

    Some industry professionals are of the opinion that the sophisticated worm known as Stuxnet was created for the purpose of launching a cyberattack.

    How to Tell If Your Computer Has a Worm ?

    Most of the time, it’s difficult to detect if there is a computer worm present in the system. Unless you have an antivirus software. But there are some techniques that we can use to check if there is a computer worm is present in the system 

    1. Hard Disk Space

    Basically, computer worms replicate themselves exponentially, which means free disk space in the system would be eaten up. Regular check in the memory space and if there is an unwanted spike in the memory space, it’s a good time to it. 

    2. Performance

    Computer worms tends to slow down the system, by globing up the processing power for it’s replication process. If programs in the systems are crashing/not running as expected without a valid reason, Then It’s a red flag. 

    3. Missing/Corrupted Files

    The most malicious computer worms prone to delete files in the system or corrupt them and making it inaccessible. If the files are deleted without a prior consent, then it’s a time to probe more.  

    4. New Temporary Files

    A computer worm creates a temporary file the user did not download or create in their storage. These files can contain worm’s nomenclature, random characters or a string of encrypted characters. These files may delete themselves if clicked on, or after a certain period of time or perform certain unwanted illicit actions. 

    5. Malicious Emails

    One ominous sign of a computer worm is finding emails sent out with the user’s address that they didn’t intend to. These emails often contain malicious attachments or spam links that spread the worm even further, compromising the victim’s contacts and name.

    How to Stop Computer Worms?

    Infiltration of Computer worms can be controlled to a great extent by following best security practices. To help protect your computer/gadgets from computer worms and other online threats, take these steps. 

    Most software vulnerabilities that are out in the wild are major infection vectors for computer worms. Ensure computer/smart gadgets operating system and applications are up to date with the latest versions. Install the updates as soon as they’re available, the software vendors would ship bug fixes, and security patches in the update and this would be helpful in addressing zero-day vulnerabilities. 

    Social Engineering is another popular way for hackers to spread worms (and other types of malwares). Always be extra cautious when accessing unsolicited emails/Instant messages especially those from unknown senders that contain attachments or dubious links. Most of the social engineering happens either for a favour or money or unwanted urgency intentions i.e. winning a lottery/Urgent help etc. be cognizant to these cues. 

    Build a stealth internet security software solution that can help block these threats. Investing in this security solution would be a great asset for corporates. A good product should amalgamate anti-phishing technology as well as defences against viruses, spyware, ransomware, computer worms and other online threats 

    Personal Security protocol is something every individual practice, keep your passwords safe, follow 2-factor authentication, use VPN when connecting to public Wi-Fi, don’t share passwords over emails/chats, use encrypted file transfer and sanitize your password every 90 days. 

    Below is a ideal mitigation plan to deal with computer worms 

    • Isolate the device. Put the gadget in isolation. First, separate the contaminated gadget from the others. Worms can propagate across local area networks (LANs); thus, you should unplug the infected device from the internet and remove it from the LAN. 
    • Evaluate the level of spread. The next step is to use your antivirus software to check all your other devices to determine whether the worm has already spread. If it has, you will need to quarantine any more infected devices before continuing to steps three and four. 
    • Work on removing the computer worm. The computer worm must be eliminated in the following stage. Most antivirus programmes that can identify computer worms are also able to eliminate them. Many antivirus programmes have the capability to automatically delete malware or place it in quarantine after they have identified a worm. 
    • If necessary, make use of a software that is specifically designed for worm removal. There are worms that are more obstinate than others. If your antivirus software is unable to remove it, you should do a search on the internet for a worm-removal programme that is unique to the kind of worm that is present on your system. The scan log created by your antivirus software ought to provide indication about the nature of the infection. 

    Difference between Worm, Virus, Trojan Horse

    ViruswormTrojan horse
    ObjectiveContaminate the host systemEat/Reduce/Kill the system resourceSteal the information from the system
    Remote controlNot PossibleYesYes
    Spread mechanismExecutable filesexecuted due to the weaknesses in systemexecutes through a program and interprets as utility software
    Speed of contagionModerateFastModerate


    It is important to remember that computer worms can attack your computer, as they are normally unwanted programs (malware) that are created to take over the functionality of a computer. A computer worm is a program that replicates itself via network connectivity. It infiltrates other computers without the knowledge of the owner by exploiting security holes. Worms share some characteristic with viruses but are not a subset of viruses, whereas the latter may have specific function(s) outside of replication or spread.  

    Computer worms are advanced, they're getting smarter, and they're nearly impossible to stop. The only way to protect your computer is to prevent other people from being infected by the worm. 

    Most worms simply copy themselves to the target computer, only to do the same thing again. They're not very intelligent, as they are built to run in a very specific manner and that's pretty much the end of it. However, the damage that they can cause is great. Worms have been known to destroy files completely and even delete data. If this kind of thing happens on a network, then the repercussions are severe and could affect a large number of users. A personal computer is still fair game for worm attacks, but it's more likely to result in only local damage than if it were a business or company server. Bottom line: Keep your operating system up to date, ensure you follow best security practices and you'll be protected from most worm activity by default.

    Frequently Asked Questions (FAQs)

    1Are computer worms harmful?

    Not all worms are malicious, they are worms like helpful worm or anti-worm, which is used for research and testing purpose. 

    2How do computer worms work?

    A computer worm does a self-replication itself and infects to other computer by leveraging network/OS loopholes and spreads exponentially.

    3How do people get computer worms?

    Social Engineering, Phishing, and malicious links are the major issues for people getting into computer worms.

    4Do computer worms still exist?

    Yes, computer worms still exists, The worms are modified and rebuilt by the hacker to make it tedious to detect.


    DhineshSunder Ganapathi


    DhineshSunder Ganapathi is an experienced Software Engineer in Data-Platform, Data Integrations, and Backend Technologies with a demonstrated history of working in the information technology and services industry. He has a prolific knowledge of Python, Flask, FASTAPI, Mysql, Airflow, AWS, Docker, REST APIs, Shell-scripting, and Distributed Systems. In addition, Dhinesh is a budding author, a tech blogger, a chess evangelist, and a candid toastmaster.

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