What Is a Computer Worm?
A computer worm is a type of malware that self-replicates once it reaches the victim’s device.
Its main function is to spread from an infected device to other devices by replicating itself endlessly. It usually achieves this by exploiting the device’s OS (operating system) in subtle and invisible ways.
A worm’s key feature is that it does not need human activation or guidance to spread or self-replicate. Once it breaches a system, it’ll follow it subroutines and begin replicating and spreading throughout the network.
Worms will spread via online networks as well as physical connections (through USB) and will keep replicating in any medium they’re in.
How Do Computer Worms Spread?
Worms are variants of Trojan horses, so their attack vectors are varied and insidious, with most users not realizing what happens.
Here are the main ways a worm spreads across devices:
- Phishing – Hackers can infect malicious emails with worms by inserting them into attachments or links. Once the victim opens the attachment or clicks the link, the worm is covertly inserted into the victim’s device and is free to replicate
- Networks – Worms will self-replicate and spread across entire networks by exploiting the “shared access”
- File Sharing – P2P networks (torrenting) can carry worms in the files you download
- External devices – Worms can also spread across physical devices like external hard drives and USB sticks
- Security Holes – Worms can also exploit security vulnerabilities in a system to find an entry point on the device
- Installer Downloads – Downloadable software installers may also be worms in disguise, so be careful where you download things from
- IoT Devices – In a controlled experiment, researchers could infect an IoT device with a worm, which then spread to a neighbor’s IoT devices
The most common computer worms spread via email. Once they’re on your device, they’ll access your email client and copies of itself to all your email contact list.
Once your contacts open your email, the worm will spread to their devices too, and keep doing this until it cannot spread anymore.
Emails containing worms that are sent by hackers will employ social engineering to manipulate you into opening the infected links or downloading the infected attachments.
Other worms will spread via instant-messaging apps like WhatsApp or Telegram. Once they’ve infected your device, the worms can access these apps and send copies of itself to all your contacts.
It’ll auto-create clickbait messages like “HEY, you HAVE to check this out” written in caps lock to attract attention and encourage them to click.
Internet worms are the most insidious, though. Hackers use them to target specific vulnerabilities in operating systems and devices. These are targeted attacks that have clear entry points and waste no resources infiltrating a device.
What Can a Worm Do Once It Reaches a Device?
A computer worm will go through multiple stages once it’s released into the wild and until it reaches a device:
1. System Entry
Stage 1 is the system entry, where the worm manages to gain access to a device either through an unsecured local network, an OS vulnerability, or through any of the other attack vectors.
Once it gains entry, a worm will begin Stage 2, which is when the real damage begins to unfold. It’s also the stage at which you have to act quickly to remove the worm from your device before it’s too late.
Once inside a device, the worm will begin Stage 2, which is replicating uncontrollably everywhere on the device where it won’t be discovered.
It will also start looking for entry points into other devices or on the local network, to see if it can infect other devices.
A worm is most dangerous once it begins replicating because it can produce a lot more damage the more numerous it is.
3. Hiding and Attacking
Stage 3 is when the worm will hide on your PC and begin attacking your device while remaining undetected for as long as possible.
In the meantime, the worm is in constant state of self-replication, spreading, and attacking your device.
Here’s exactly what a worm can do to your device:
- Delete files. Depending on its instructions, the worm can delete any file on your computer
- Steal data. The hacker can instruct the worm to steal specific data (financial data) and send it to the hacker
- Consume bandwidth. The worm can slow down your internet connection by stealthily consuming your bandwidth
- Consume your hard drive space. Worms can make it look like your hard drive is out of space
- Open a backdoor. A worm can create a security vulnerability (backdoor) for the hacker to send other malware like keyloggers and phishing tools
- Bring other malware with it. The worm can install spyware or ransomware once it breaches your device
- Spread through email and instant messaging apps. The worm can spread itself via email and instant messaging apps to all your contacts
A very common use of worms is to deliver a “payload” of code that creates a backdoor into a system. The hacker can then take control of the system or install other malware in it.
They can even turn that device into a “zombie device” that becomes part of a botnet to be used in a DDoS attack.
And it all starts from an insidious worm attack!
Types of Computer Worms
There are multiple types of computer worms, based on their attack vectors and infiltration methods. I’ve already mentioned some of these attack vectors.
- Email Worms
These worm variants will create and send emails to all the contacts in your email client. They will likely include a malicious link or attachment in the email that carries a variant of itself.
The worm will likely use phishing techniques and social engineering tactics to persuade your contacts to open the infected links or attachments.
Hackers may also place a worm in an email through several methods. These include MS Outlook services, Windows MAPI functions, and inserting the worm in the text of the email.
Email worms still remain the most effective attack vector out of all worm types.
- File-Sharing Worms
P2P file-sharing, also known as torrenting, is very dangerous from a security standpoint. It’s a preferred playground for malware, especially worms.
Hackers can disguise these worms as executable files or media files. This can mean games, movies, and especially software that you “pirate” online.
File-sharing worms are often instructed to target industrial environments like power utilities and sewage plants, if they can access them.
Cryptoworms have nothing to do with cryptocurrency. Instead, their name comes from cryptography.
These worms will encrypt the files on your system and they’re often the main element of ransomware attacks.
Hackers will encrypt and lock your files, then they will demand a ransom payment to unencrypt your files.
- Instant Messaging Worms
These worms can come from any instant message app, like Skype, WhatsApp, Telegram, Signal, and others.
They’ll take the form of attachments or links embedded into persuasive texts. Through social engineering, hackers can vary the nature of these attacks and manipulate people into clicking the malicious links or downloading the infected attachments.
Once you get the worm, it will send itself to all your social media contacts and spread onward through the network.
- Internet (Network) Worms
These worms will exploit vulnerabilities of operating systems and infiltrate whatever device they can.
Internet worms are the oldest types of worms in existence, existing since the late 20th century when the first operating systems appeared.
They will scan the internet and look for devices with known vulnerabilities. Then, once it finds one, it will infiltrate it and begin replicating.
These are all the known types of computer worms as of 2023.
These worms are relatively new because Internet-of-Things devices haven’t been around for a long time.
The Mirai worm is the most notorious of these types of worms. It infects IoT devices like smart cameras and routers and turns them into zombie devices as part of a botnet.
Once it infects an IoT device, it will look for other IoT devices on the same network or even try to access other networks through vulnerabilities.
These are all the computer worm types that are in use today. They all exploit different elements of communication and the online ecosystem to infiltrate, control, and manipulate devices.
Difference Between Worms and Other Malware
A worm is a type of malware, but not all malware are worms. There’s a difference between different types of malware. This is what we’ll explore in this section.
The most important comparison is between a worm and a virus because they’re the most closely-related and might confuse people.
Here’s the gist of it:
- Malware – a malicious code or application that is designed to harm a device or their users. Malware include adware, spyware, ransomware, and so on
- Virus – A type of malware that requires your interaction to self-replicate, spread to other apps/systems, and damage your system
- Worm – A type of malware that does not require any interaction to begin self-replicating, spreading to other systems, and damaging your OS
So, the main difference between a virus and worm is that the worm is self-sufficient and acts autonomously without external help or interactions.
Neither the hacker nor the victim has to interact with it or activate it. Once it infects a system, it will take action immediately.
Clearly, the worm is the more dangerous one between the two. It spreads faster, takes action faster, and you have less time to mitigate a worm before it damages your device.
How to Know if Your Device Has a Worm?
It’s not difficult to detect a worm infection on your device. These little buggers leave behind clear breadcrumbs that are easy to spot.
Here’s what you should be looking for:
- Your hard drive is full without explanation. That’s the worm replicating itself and filling up your storage space
- Missing files that you can’t explain. These include even personal files that you know should be there but aren’t
- Hidden files or folders. If you notice that some of the files on your device are hidden for no reason, you might have a worm
- Slow device performance. A worm will slow down your device considerably by eating up its resources
- Bad browser performance. Similarly, the worm will affect your bandwidth and slow down your browser performance
- Unusual OS behaviors like error messages out of nowhere, notification pop-ups, programs not functioning correctly
- Unrecognized programs or files that you haven’t installed. The worm will often bring other malware once it infiltrates your device
- Websites or programs opening by themselves even though they shouldn’t. This doesn’t include programs that start with the OS
- Messages have been sent to contacts in your email list or on your instant messaging apps. That’s the worm sending variants of itself to other people, trying to spread
- Firewall warnings that you can’t explain. Windows may often detect that something’s wrong but it can’t find the worm. So, it’ll send you warnings
- Your system freezing or crashing without explanation becoming a common occurrence
- Your antivirus software is sending you warnings about a threat to your device
Taken individually, none of the symptoms above might lead you to suspect a worm. But once the symptoms pile up, it becomes increasingly clear that you’re dealing with a worm.
Once you reach this stage, it’s important to remove the worm as fast as possible. Read below to see how to do that!
How to Remove a Worm from Your Device
If you’re pretty sure you have a worm problem on your PC, here’s what you should do:
- Disconnect the device from the internet or any other network. Worms will spread throughout every network connected to a device and reach everywhere. You don’t want that
- Scan every device that was connected to the original device and see if the worm has spread. If it did, then isolate those devices too by disconnecting them from the internet and other networks
- Install an antimalware tool (premium, if possible) on all the infected devices and launch a system-wide scan. The antivirus should remove every trace of the worm
- Use a worm-removal tool if your antivirus doesn’t find any trace of the worm. Some are more sophisticated and will avoid detection. You can find worm-removal tools online
There isn’t much you can do yourself manually unless you fancy reinstalling your operating system. And that’s not something most users will prefer doing, either way.
The only thing you can do once you find a worm in your system is let your security systems deal with it.
Prevention Methods Against Worms
As I always say, prevention is better than mitigation, and this is especially the case with cyberattacks that can severely impact your business if successful.
Fortunately, worms are not hard to avoid if you have surface-level knowledge and common sense when operating online.
- Don’t click on any pop-up ads when you’re browsing. Adware can often carry worms that will infiltrate your device once you click on the pop-ups
- Update all your software regularly. Outdated software may have vulnerabilities that are easily exploited by worm attacks. This is especially true for your operating system (Windows)
- Don’t open email links or attachments liberally. The golden rule is that if you don’t know who the other party is, don’t open any email attachments or links because they may be malicious
- Back up your data. If you back up your data regularly, you’ll mitigate most of the fallout in the case of a worm attack that compromises your system and files
- Use strong passwords. It’s a known fact that passwords are one of the biggest reasons for data breaches. Strong passwords can mitigate many cyberattacks and prevent many others
- Use a VPN on P2P file-sharing sites. Ideally, you should not torrent anything because you don’t know who the source is. They can sneak a malware in your files without facing any repercussions. However, if you have to, then it’s a good idea to use a VPN
- Practice common sense when you go online. Most cyberattacks occur due to human error. You click a suspicious link, download a file from an untrusted source, visit an unsecured and malicious website, and so on
- Use premium antimalware software. Your Windows security system isn’t enough to protect against cyber-threats. Premium antimalware are much more robust and sophisticated, so they will detect threats with more accuracy, quarantine them earlier, and mitigate the attack before it damages your system
Even if you don’t follow any of the above, at the very least, practice common sense and educate yourself about cybersecurity and cyberattacks.
You don’t need a Master’s Degree in cybersecurity or cybercrime to realize that a site looks suspicious or that an email attachment might be better left unopened.
These common-sense judgments are enough to protect you against most cyber-threats if you’re a common user.
An enterprise has no excuse not to use premium security solutions and be more aware of the risks they face online.