What is Malware? Definition, Types, Prevention

According to Kaspersky Malware specifically refers to malicious software, but malicious code includes website scripts that can exploit vulnerabilities in order to upload malware.

What is Malware?

Malicious software, or malware, is a term used to describe software designed to disrupt computer operations or gain access to computer systems, without the user’s knowledge or permission. Malware has become an umbrella term used to describe all hostile or intrusive software. The term malware includes computer viruses, worms, Trojan horses, ransomware, spyware, adware, scareware, and other malicious programs. Malware may be obvious and simple to identify or it can be very stealthy and almost impossible to detect.

Types of Malware

Cybercriminals target users’ end devices through the installation of malware. Click Play to view an animation of the three most common types of malware.


A virus is malicious executable code attached to another executable file, such as a legitimate program. Most viruses require end-user initiation and can activate at a specific time or date. Computer viruses usually spread in one of three ways: from removable media; from downloads off the Internet; and from email attachments. Viruses can be harmless and simply display a picture or they can be destructive, such as those that modify or delete data. In order to avoid detection, a virus mutates.  The simple act of opening a file can trigger a virus. A boot sector, or file system virus, infects USB flash drives and can spread to the system’s hard disk. Executing a specific program can activate a program virus. Once the program virus is active, it will usually infect other programs on the computer or other computers on the network. The Melissa Virus was an example of a virus spread via email. Melissa affected tens of thousands of users and caused an estimated $1.2 billion in damage. Click here to read more about viruses.


Worms are malicious code that replicates by independently exploiting vulnerabilities in networks. Worms usually slow down networks. Whereas a virus requires a host program to run, worms can run by themselves. Other than the initial infection, worms no longer require user participation. After a worm affects a host, it is able to spread very quickly over the network. Worms share similar patterns. They all have an enabling vulnerability, a way to propagate themselves, and they all contain a payload.

Worms are responsible for some of the most devastating attacks on the Internet. For example, in 2001, the Code Red worm infected 658 servers. Within 19 hours, the worm infected over 300,000 servers.

Trojan horse

A Trojan horse is malware that carries out malicious operations under the guise of a desired operation such as playing an online game. This malicious code exploits the privileges of the user that runs it. A Trojan horse differs from a virus because the Trojan binds itself to non-executable files, such as image files, audio files, or games.

Logic Bombs

A logic bomb is a malicious program that uses a trigger to awaken the malicious code. For example, triggers can be dates, times, other programs running, or the deletion of a user account. The logic bomb remains inactive until that trigger event happens. Once activated, a logic bomb implements a malicious code that causes harm to a computer. A logic bomb can sabotage database records, erase files, and attack operating systems or applications. Cybersecurity specialists recently discovered logic bombs that attack and destroy the hardware components in a workstation or server including the cooling fans, CPU, memory, hard drives, and power supplies. The logic bomb overdrives these devices until they o overheat or fail.


Ransomware holds a computer system, or the data it contains, captive until the target makes a payment. Ransomware usually works by encrypting data in the computer with a key unknown to the user. The user must pay a ransom to the criminals to remove the restriction.

Some other versions of ransomware can take advantage of specific system vulnerabilities to lock down the system. Ransomware propagates as a Trojan horse and is the result of a downloaded file or some software weakness.

Payment through an untraceable payment system is always the criminal’s goal. Once the victim pays, the criminal supplies a program that decrypts the files or sends an unlock code. Click here to read more about ransomware.

Backdoors and Rootkits

A backdoor refers to the program or code introduced by a criminal who has compromised a system. The backdoor bypasses the normal authentication used to access a system. A few common backdoor programs are Netbus and Back Orifice, which both allow remote access to unauthorized system users. The purpose of the backdoor is to grant cyber criminals future access to the system even if the organization fixes the original vulnerability used to attack the system. Usually, criminals have authorized users unknowingly run a Trojan horse program on their machine to install the backdoor.

A rootkit modifies the operating system to create a backdoor. Attackers then use the backdoor to access the computer remotely. Most rootkits take advantage of software vulnerabilities to perform privilege escalation and modify system files. Privilege escalation takes advantage of programming errors or design flaws to grant the criminal elevated access to network resources and data. It is also common for rootkits to modify system forensics and monitoring tools, making them very hard to detect. Often, a user must wipe and reinstall the operating system of a computer infected by a rootkit.

Defending Against Malware

A few simple steps can help defend against all forms of malware:

  • Antivirus Program – The majority of antivirus suites catch the most widespread forms of malware. However, cybercriminals develop and deploy new threats on a daily basis. Therefore, the key to an effective antivirus solution is to keep the signatures updated. A signature is like a fingerprint. It identifies the characteristics of a piece of malicious code.
  • Up-to-Date Software – Many forms of malware achieve their objectives through the exploitation of vulnerabilities in software, both in the operating system and applications. Although operating system vulnerabilities were the main source of problems, today’s application-level vulnerabilities pose the greatest risk. Unfortunately, while operating system vendors are becoming more and more responsive to patching, most application vendors are not.

About Adamu Maigari

My name is Adamu Maigari, I'm living in Borno, Nigeria - I write on Tech, Crypto, Gaming, Computing, Cybersecurity, and How to make money online.

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