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What Is Malicious Code?

By DeVry University

September 2, 2022

5 min read

Cybercriminals utilize a wide array of tactics to accomplish their goals, and malicious code is often one of them. But exactly what is malicious code and how harmful is it?


Malicious code is a broad category of dangerous programs, files and code strings that are used to create malicious software, also known as malware, and carry out a cyberattack. There are several different types of malicious code, each with various effects, uses and methods of attack.


Malicious code can include everything from full software programs like keyloggers or spyware to a small computer virus that prevents your device from functioning correctly. And just as there are many types of malicious code, there are different levels of damage it can cause.


When asking “what is malicious code?”, it’s also important to understand its different forms and how to defend against attacks that could threaten your devices and data.


In this article, we’ll explore these concepts in the following sections:

What Is a Possible Effect of Malicious Code?

Malicious code can pose a wide range of security threats. It works by infecting your computer with unwanted files, programs or lines of code that can impede its ability to function. It can also steal your data or carry out commands by running malicious scripts without detection.

Malicious code can also lock down your computer, allow cybercriminals to gain remote access to it or otherwise impact its ability to work properly. Chances are that you’ve used a computer infected by one of these viruses and have firsthand experience with the frustration they can cause. When multiple computers in an organization’s network have been infected, malicious files can have a significant impact on productivity and output.

Malicious code can be used to steal private information like passwords and payment profiles, or enable identity theft. It can be introduced by a seemingly innocent email attachment or link sent by a hacker in a phishing attack targeting a broad population, or a spear phishing attack targeting one person.

But cybercriminals do not limit their targets to individuals. The impact of cyberattacks may be worse when companies and their computer systems, often holding great amounts of data, come under threat. Malicious code attacks can be used to break into an organization’s data systems and result in security breaches that put sensitive customer data at risk. Cybercriminals sometimes use botnets (networks of hijacked computer devices) to distribute malware, crash servers or steal data.

Different Types of Malicious Code

The wide variety of malicious code types makes it even more important to understand how each type works and how you and cyber security professionals can safeguard computers, networks and sensitive information.

Here are a few examples of malicious code and what they do:

  • Keyloggers: Keyloggers track your keystrokes when you’re typing your passwords or other sensitive data into third-party websites to steal information or gain access.

  • Spyware: Spyware infects your computer by searching your files for sensitive data and covertly transferring it.

    • Trojan horses: Trojan horses pose as legitimate software in order to trick you into installing malware.
  • Adware: Adware displays unwanted ads on your screen.

  • Ransomware: Ransomware seizes your personal files and encrypts them before demanding payment to restore them.

    • Rootkits: Rootkits provide unknown users access to your device without being detected.
  • Worm viruses: Worm viruses replicate themselves within your device, and then spread to others on the same network.

  • Cross-site scripting: In cross-site scripting attacks, malicious code is injected into the content of websites that a computer user would normally trust, allowing the attackers to spread malware, phish for credentials or even re-write the contents of a website.

How Widespread Is Malicious Code?

While many people are still wondering “What is malicious code?” those involved in the cybersecurity world know the answer all too well. In fact, according to, there are currently more than 1 billion pieces of malware installed around the world.

Common targets for malicious code encompass large-scale components like computer networking infrastructure and small components like mobile or desktop apps. Any device that uses a computer to operate it can be infected. The connectivity found in everything from the smart IoT devices many of us have in our homes, to network devices like routers, modems and servers, to desktop and laptop computers can create a “gateway” for bad actors who exploit its vulnerabilities.

How Can You Avoid Downloading Malicious Code?

Even if you’re not a cyber security professional, there are plenty of steps that you can take to help keep yourself safe from malicious code while you’re online, including:

    • Install robust anti-virus and malware protection software.
    • Download files or plug-ins only from places you recognize and trust.
  • Double-check the URL before clicking on anything from a website.

  • Keep your operating system (OS) and antivirus software up to date.

  • Enable two-factor authentication whenever possible.

    • Download apps only from your phone’s official app market.
    • Install an ad or pop-up blocker to your browser.

If you still end up downloading something with malicious code, there’s no need to panic. Disconnect the infected device from the internet, then search through all your files for anything that looks unfamiliar and delete them immediately. If you’re not sure what you’re looking for, you may want to run an antivirus scan to identify and remove any malicious codes or software for you.


If you’re still in doubt, reach out to a computer specialist to make sure the malicious code is removed from your device.

Ready To Learn How To Defend Against Cyberattacks?

Now that we’ve answered the question “What is malicious code?”, the idea of fighting cybercrime may sound like an exciting career path. If you’re ready to pursue a career defending devices and networks against malicious code, our cyber security degree programs can help you get started.

We offer four unique programs to help you focus your interests while preparing to pursue a career in cyber security, including our Undergraduate Certificate in Cyber Security, Associate in Cybersecurity and Networking, Bachelor’s in Information Technology with a Cyber Security Specialization and Bachelor’s in Computer Information Systems with a Cyber Security Programming Specialization. Classes start every 8 weeks.

8-Week Class Sessions

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