Computer worms: What they are and how to protect your Mac

Q: What is the biggest danger of a computer worm?

The biggest danger is that a computer worm can spread on its own. Once it infects one vulnerable device, it can quickly spread to others before anyone notices. Some worms also install ransomware, spyware, or other malware, causing even more damage.

Q: How is a worm different from a virus?

Both worms and viruses are types of malware, but they spread differently. A virus attaches itself to another file or program and usually needs someone to open it. A worm is a stand-alone program that can copy itself and, in some cases, spread automatically by exploiting security weaknesses.

Q: Can computer worms spread without user interaction?

Yes. Some computer worms can spread without anyone clicking a link, opening a file, or installing an app. They find vulnerable devices and exploit security weaknesses to spread automatically. Others need someone to open an infected file first before they continue spreading.

Q: Are computer worms still a threat?

Yes. Large worm outbreaks are less common today, but computer worms are still a threat. Many modern malware attacks use worm-like spreading to infect more devices. Keeping your Mac and apps up to date is one of the best ways to reduce the risk.

Computer worms copy themselves and spread between vulnerable devices
Some worms can spread without anyone opening a file
Worm infections may slow devices, steal data, or install more malware
Updates and antivirus protection help reduce the risk

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What is a computer worm?

A computer worm is a type of malware that copies itself and spreads from one device to another. Unlike many other threats, a worm doesn’t always need you to open an infected file or install an app. It can find security weaknesses in a network and spread to other devices on its own.

Some worms are delivered through email attachments, shared folders, messaging services, removable drives, or poorly secured networks. Once inside a device, a worm may simply keep copying itself, consuming storage, memory, and network capacity.

More harmful worms can also steal information, damage files, install other malware, or add the device to a botnet. Worms have affected Windows computers more often, but Macs can also be at risk, especially if software isn't kept up to date or files are shared across connected devices.

Network worms

Network worms search for vulnerable devices connected to the same local network or the internet. They can spread quickly when several computers share the same unpatched security weakness.

Email worms

Email worms arrive through malicious attachments or links and may send copies of themselves to saved contacts. They often depend on someone opening the first infected file.

Messaging worms

These worms spread through chat apps, social media, or direct messages. They may send infected links or files from an account you already know and trust.

File-sharing worms

File-sharing worms place copies of themselves in shared folders or disguise themselves as popular files. Someone may download and open the infected file without realizing it's malicious.

Removable-drive worms

Some worms copy themselves to USB drives or external storage. They can reach another computer when you connect the infected drive and the malicious file is opened or launched automatically.

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How does a computer worm work?

The details vary, but most worms follow the same basic pattern: they enter one device, create copies of themselves, and look for additional systems they can reach.

The worm gets in

A worm gets onto a device through an unsafe email attachment, a malicious download, a USB drive, an exposed network service, or an unpatched security weakness.

It starts running

Once active, the worm installs or runs its code. It may hide in the background, change system settings, or take steps to remain active after the computer restarts.

It searches for targets

The worm checks the local network, address book, shared folders, removable drives, or internet-facing devices for other systems it may be able to reach.

It copies itself

When the worm finds a suitable target, it sends or installs another copy. A vulnerable device may become infected without you downloading or approving anything.

The cycle continues

Each newly infected device begins searching for more targets. This automatic copying can let a worm spread rapidly through homes, businesses, and large computer networks.

What are real-world examples of computer worms?

Some worms have spread so widely that they changed how people protect computers and networks. Most of these worms affected Windows or older Unix computers, but they show how quickly a worm can spread and cause problems.

Morris worm, 1988

The Morris worm was one of the first major internet worm outbreaks. It took advantage of security weaknesses in Unix computers and kept making copies of itself. This slowed down or stopped many computers from working. It affected about 10% of the computers connected to the internet at the time and led to the creation of the first Computer Emergency Response Team.

Conficker, 2008

Conficker spread through Windows computers that were missing an important security update. It also spread through weak passwords, shared folders, and USB drives. Once installed, it could disable security services and prevent infected computers from reaching some security websites. It also connected large numbers of compromised devices, creating one of the most significant botnets of its time.

WannaCry, 2017

WannaCry combined ransomware with worm-like spreading. It exploited a patched vulnerability in older Windows systems and moved automatically between vulnerable computers. The outbreak reached hundreds of thousands of devices across more than 150 countries, disrupting hospitals, businesses, transport services, and government organizations.

What are the risks and impacts
of computer worms?

A worm doesn’t have to destroy files to cause damage. Just by making copies of itself, it can slow down devices and networks. Some worms also install other malware that can cause even more damage.

Slower devices

As a worm keeps making copies of itself, it uses your Mac's memory, processing power, and storage. An infected computer may become slow, unstable, overheated, or difficult to use.

Network disruption

A worm keeps searching for other devices it can infect. This creates extra network traffic, which can slow down your home or work network and interrupt your internet connection.

Additional malware

Some worms install other malware after they infect a device. This can lead to stolen personal information, encrypted files from ransomware, spyware, or attackers gaining remote access to your computer.

Wider infection

A worm can spread from one infected device to others on the same network. It may then infect family computers, shared workplace systems, servers, or connected storage devices.

Who is most at risk from
computer worms?

Any connected device can be targeted, but worms spread most easily where updates, network controls, or security protections are missing.

Devices with outdated software

Computers running unsupported or unpatched software may contain known security flaws that worms are already designed to exploit.

Shared networks

Homes, offices, schools, and public organizations with many connected devices give worms more potential targets once one machine becomes infected.

Small businesses

Small businesses often have many connected devices but fewer IT resources to monitor threats, install updates, and stop a worm before it spreads.

People who share files often

People who regularly exchange attachments, USB drives, shared folders, or downloaded files have more opportunities to encounter an infected copy.

Devices without security protection

Computers that don't use antivirus software or other security tools are more likely to become infected and less likely to detect a worm before it spreads.

How can you prevent computer worms?

No single step blocks every type of worm. Combining regular updates, careful file handling, network controls, and malware protection gives you a stronger defence.

Install security updates

Keep macOS, browsers, apps, routers, and other connected devices updated. Security patches close known flaws before worms can use them to spread.

Use antivirus protection

Real-time antivirus software can help identify known worm files, malicious downloads, and other malware before they run or spread further.

Check unexpected files

Don’t open surprising attachments or shared files simply because they appear to come from someone you know. Their account or device may be infected.

Secure your network

Protect your Wi-Fi with a strong password, update your router, and turn off file sharing or remote access unless you genuinely need it.

Scan external drives

Treat USB drives and other external storage carefully. Scan unfamiliar devices and files before opening them, especially when they’ve been used on several computers.

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How Intego helps protect your Mac from computer worms

Worms are malware, so the most relevant protection starts with detecting unsafe files and preventing malicious code from running on your Mac. Intego ONE Complete combines Mac-focused antivirus protection with firewall features that help detect malware and alert you to unexpected app connections. Keep in mind that antivirus software can't replace macOS or app security updates, so it's important to install updates as they become available.

Real-time protection

Intego’s antivirus monitors your Mac for known malware and can block malicious files when they’re opened, copied, or run.

Flexible scan options

Quick, Full, Custom, and Scheduled scans let you check your Mac, selected folders, external drives, and other connected storage for threats.

Secure quarantine

If Intego finds a suspicious file, it can move it to quarantine so it can't run while you decide whether to remove or restore it.

Connection control

Intego’s Firewall shows which apps are trying to connect to networks and lets you block connections from apps you don't recognize or trust.

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Frequently asked questions

What is the biggest danger of a computer worm?

How is a worm different from a virus?

Can computer worms spread without user interaction?

Are computer worms still a threat?

Can antivirus software detect worms?

Antivirus software can detect many known computer worms, related malware files, and suspicious components they try to install. Real-time protection may block a worm before it runs, while a full scan can help find files that are already present. Detection isn’t guaranteed for every new or heavily modified threat, so antivirus protection should be used alongside software updates, secure network settings, strong passwords, and careful file handling.

Can a computer worm be removed?

Yes, but remove it carefully because the worm may have spread to other devices or installed additional malware. Disconnect the affected computer from the network, stop using shared drives, and run a full scan with updated antivirus software. Remove or quarantine anything detected, update the operating system and apps, and scan other connected devices. If the infection affects a workplace or multiple devices, you may need help from an IT professional.

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