Malware Explained: Types, Risks, and How to Protect Your Devices

Malware is a software designed to harm devices, networks or other digital systems. In other words, malware is a program that modifies other computer programs by inserting its own code to damage data or perform unauthorized actions. Its purpose is to actively monitor, steal or lock data, damage files or give the attacker access to sensitive information.

The term is short for malicious software.

Malware is not a single program. It is a wide collection of viruses, worms, ransomware, spyware and other malicious software. NIST defines malware as a program or software that aims to perform unauthorized actions that impact a system’s confidentiality, integrity or availability to a larger extent.

Understanding malware is important because preventing an attack is less complicated than recovering from one. Hence, this guide describes the types of malware, how it occurs, warning signs to look out for, steps to follow a suspected infection and how to reduce the damage caused by it.

If you want to strengthen your overall security level beyond malware protection, see our Cybersecurity Guide for broader cybersecurity best practices.

What Is Malware?

Malware is malicious software designed to harm, spy on, disrupt, manipulate or gain unauthorized access to a device or system.

Its purpose depends on the attacker. Malware may be used to:

Steal passwords or financial information.
Monitor what a person does on a device.
Encrypt files and demand payment.
Delete or alter data.
Install other malicious programs.
Give an attacker remote access.
Use a device as part of a larger attack.
Collect confidential business information.

The primary target of malware can be laptops, desktop computers, smartphones, servers and other digitally connected systems. NIST defines the wider category of the malware that includes viruses, worms, ransomware, Trojan horses, spyware and other types of physical social engineering.

Common Types of Malware

Different forms of malware spread and behave in different ways. Knowing the distinction helps explain why one security measure cannot stop every attack.

Malware Type	What It Generally Does
Virus	Attaches itself to another file or program and spreads when that infected program runs
Worm	Can spread between systems without attaching itself to a host file
Trojan	Pretends to be legitimate or useful software while hiding malicious behavior
Ransomware	Blocks access to files or systems, often through encryption, and demands payment
Spyware	Secretly collects information about a user or device
Keylogger	Records keyboard input, potentially capturing passwords and messages
Rootkit	Helps attackers hide malicious activity or maintain privileged access
RAT	Gives an attacker remote-control capabilities over a compromised device
Adware	Displays unwanted advertising; some forms may also behave maliciously.

How Does Malware Get Onto a Device?

Malware doesn’t infect the systems in the same way. In some cases, attackers exploit the technical bug or vulnerability, trick the users into opening harmful content, threaten users of their stolen credentials or incorporate several other techniques.

Most of the commonly used infected paths include:

Phishing Messages

In this case, the attacker sends a text message, or an email, or by any other means of communication that includes a malicious link or attachment.
CISA has warned that phishing attempts frequently try to convince users to click on a malicious link or share their personal information.
Malware is not included in every suspicious email. Occasionally, the attacker’s intent is only to steal the login credentials. Others may lead to malware installation.

Malicious or Compromised Downloads

Software that is downloaded from a source that is not trustworthy may have a malicious code that is hidden.
Well-known examples of this risk can be seen in pirated software, fake installers, app packages that are unofficial, fraudulent browser extensions or programs that are distributed across the websites that are compromised.
A file name or an icon doesn’t mean that it is secure.

Unpatched Software Vulnerabilities

Security vulnerabilities in the applications, system software, operating systems and browsers can sometimes act as an entry point for the attackers.
The timely security updates released by the security vendors fix these known weaknesses. Therefore, CISA strictly recommends installing the software updates as soon as they are released instead of delaying them.

Compromised Accounts

Malware attacks do not always start with a user downloading a suspicious attachment or file.
Attackers often use the stolen credentials to get into the system and access the services remotely and then set up malicious tools. Ransomware guidance from CISA strongly recommends identity controls and phishing-resistant multifactor authentication to lower the risks from such compromised credentials cases.

Removable Devices

A USB drive or any other media that can be removable can carry the malicious code.
This is not noticeable compared to email-based attacks to many users, but the malware is capable of infecting removable devices by spreading through the system or collecting sensitive information.

What Are the Signs of a Malware Infection?

There is no single symptom that proves a device has malware.

Some malware deliberately tries to remain invisible. Other infections cause obvious disruption. Possible warning signs include:

A device suddenly becomes much slower.
Applications repeatedly crash.
Unexpected pop-ups or browser redirects.
Security software being disabled without explanation.
Unknown programs appearing.
Browser settings changing unexpectedly.
Unusual network or processor activity.
Files disappearing, changing or becoming inaccessible.
Accounts showing logins you do not recognise.
Messages being sent from your accounts without your knowledge.
A ransom message appeared.
Unexplained changes to system settings.

These above mentioned signs can be treated as warnings rather than proof. Hardware issues, software vulnerabilities, low storage, and legitimate background processes can also cause similar behaviour.

A device that contains malware can also seem to work exceptionally well without showing obvious symptoms.

What Should You Do If You Suspect Malware?

The answer to this question depends on whether the device that is affected by malware is a personal computer, a company-owned device or part of a larger network.

1. Disconnect the Device if an Active Infection Is Suspected

If your device appears to be infected with malware, and you notice the sensitive information is being stolen or the files are being encrypted, disconnect the infected device from the network. This can help reduce movement or other data.

For organizational ransomware incidents, CISA recommends disconnecting the affected system from the network and shared drives.

For a company-owned device, an organisation’s incident response policy needs to be followed rather than making the changes on your own.

2. Tell the Appropriate Security or IT Contact

Employees of an organization should report the suspected activity without any delay.

An organization’s security team may need to review the system logs or any other evidence to know what happened. Reading files, reinstalling the operating system or running multiple cleanup or antivirus tools before reporting malware can only make the investigation more difficult and sometimes may lose the crucial evidence.

3. Run Trusted Security Software

Make sure to use valid antivirus and anti-malware software from a trusted source. NIST describes antivirus software as the program that helps in identifying major types of malware and managing or containing malware incidents. Do not try to install a random “malware remover” that is advertised through a website browser pop-up. Security software that is fake can itself be harmful to the device.

4. Change Compromised Passwords From a Clean Device

If you assume that your login credentials may have been compromised, immediately change the passwords using a trusted device.

Sensitive accounts need to be prioritized such as:

Primary email
Online banking and payment services
Accounts used for work
Cloud storage
Social media
Password managers or authenticators

Make sure to use a unique password for each account, and multifactor authentication needs to be enabled where available.

5. Restore or Rebuild the Device When Necessary

Deleting a malicious file does not always confirm that every other area of the device is safe. When the device is seriously compromised, you may need to restore the data from a good backup or by reinstalling using trusted installation media. In the case of an organisation dealing with malware, they should follow the established incident response plan and recovery procedures.

Frequently Asked Questions About Malware

1. Does Clicking a Malicious Link Always Install Malware?

No. Not every malicious link carries the same motive. Every link can serve different purposes. One link may lead to a fake login page, another might start a malicious download, exploit a software vulnerability or may steal sensitive information about visitors.

Whatever the intended purpose is, clicking suspicious links should be avoided.

2. Can Malware Spread Over a Network?

Yes, some malware can move across the devices and spread between connected devices in a shared network. The process depends on the software vulnerabilities, network configurations, malware and login credentials.

3. What Is the Best Way to Avoid Malware?

There is no perfect defence to avoid malware. The strongest strategy would be the combination of the software updates, strong authentication methods, recoverable backups and cautious handling of downloads or emails.

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