What is malware?

Malware refers to malicious software that’s planted on someone else’s computer, often causing significant issues. The most widely recognized types of malware include viruses, Trojan horses, and worms.

What is malware?

Malware is a general term for malicious programs that can be smuggled onto a computer and perform unwanted actions there. The term is a combination of “MALicious” and “softWARE.” It is distinct from faulty programs that may cause errors or crashes due to compatibility issues with an operating system. Malware is deliberately designed to infiltrate devices or networks with the aim of causing harm, sometimes operating unnoticed for extended periods and inflicting substantial damage. Antivirus programs and firewalls are often effective in thwarting malware attacks.


Find valuable tips to secure your computer from malware in our Digital Guides. Learn how to protect yourself from ransomware, spyware or scareware or how to detect malware, among other things. We also explain how to protect your website from malware.

What are the types of malware?

There are various types of malware, some of which differ massively from one another. It’s important to understand the programming and intentions of a malicious program, especially when it comes to dealing with it properly. The best-known types include viruses, Trojans and worms. Some malware programs also combine different types. The best known are:

Computer viruses

The term “virus” is often used interchangeably with malware, although it’s not always accurate. Computer viruses do constitute a significant portion of malware, but there are distinctions even among viruses. What all computer viruses share in common is their ability to replicate themselves, spreading autonomously within a system or across a network. The objectives of these viruses can vary. Some aim to compromise, overwhelm, or even disrupt a system, while others primarily operate covertly to spy on systems and capture sensitive data, for instance. Viruses represent the oldest form of malware.

Trojan horses

Another very well-known type of malware is the Trojan horse, which is often referred to as Trojan for the sake of simplicity. This name draws from Greek mythology, where a wooden horse concealed soldiers who infiltrated the city of Troy unnoticed. This type of malware works in a very similar way as it pretends to be a harmless or perhaps even useful program. Once installed, Trojan horses covertly surveil the host system, replicate data, or create pathways for other types of malware. Some of these malicious programs even allow remote control of the compromised system.

Computer worms

Computer worms share similarities with malware such as computer viruses but are even more self-reliant. Unlike viruses that attach to other files, worms don’t need a host file. They copy and spread on their own and can then cause great damage or copy data in a system. They spread via networks, external data media, emails or messaging services.


Ransomware gains access to a system and encrypts files. As a result, users can no longer access the data. A notification informs them that full access to their system will only be restored upon payment of a ransom. Consequently, the name of this malware is derived from “ransom.” However, it is strongly recommended not to comply with these demands as there are no assurances that the cybercriminals will actually decrypt the data after payment. You can find instructions on how to remove Ransomware in our Digital Guide.


Spyware is used to secretly spy on other people’s computers or systems. The data obtained in this way is then either used for their own purposes or passed on to third parties. This malware does not have a direct negative impact on the system; damage is rather caused by the fact that sensitive data can fall into the wrong hands.


The term scareware is derived from the word “scare”. Users are shown fake warnings that are intended either to worry them or to encourage them to download a program against a supposed threat. Once downloaded, it often installs further malware on the computer.

Examples of well-known malware

Malware is thus divided into different subtypes. It’s likely that you’ve already heard or read about specific malware programs. The best-known include:


The precursor to many subsequent computer viruses was ILOVEYOU. In 2000, this malware was distributed via email and opened by numerous unsuspecting users. Upon activation, it rapidly replicated itself, sending copies to other contacts and inflicting significant damage to systems. ILOVEYOU heightened awareness about the threat posed by computer viruses.


Emotet, a Trojan horse initially discovered in 2014, operates by copying email addresses, sender names, and headers to craft deceptive emails. When recipients click on the attachments, additional malware is installed, capable of either crippling systems or stealing sensitive information such as bank details.


The MyDoom computer worm has been targeting Windows computers since 2004, causing an estimated $40 billion in damages. Its origins remain unclear, although a line of code within it reads, “andy; i’m just doing my job, nothing personal, sorry”. This worm replicates and spreads copies via email. At its peak, MyDoom even managed to slow down the global internet by 10 percent. Initially, it primarily targeted Microsoft and the SCO Group.


WannaCry is the name of a malicious program that garnered worldwide attention in May 2017. This ransomware encrypted files on thousands of computers and demanded a $300 Bitcoin ransom for each decryption. It exploited a Windows security vulnerability. As a result, the British healthcare organization NHS had to delay critical surgeries due to inaccessible patient records. Global companies like Nissan, FedEx, and Deutsche Bahn also suffered from the malware, causing an estimated four billion dollars.


The Pegasus spyware, developed by the Israeli NSO Group, is primarily employed for surveillance on iOS and Android smartphones. NSO Group’s clients are predominantly states, and they claim to use the software solely for crime detection and counterterrorism purposes. However, there has been significant criticism of this spyware, as it is suspected that some countries may also use it to monitor opposition figures or individuals critical of the government.

BKA Trojans

The BKA Trojan is a hybrid of scareware and ransomware. When users booted up their computers, they were greeted with a full-page advertisement in place of the usual home screen. The ad falsely claimed that the Federal Criminal Police Office had discovered child pornography on the computer, among other things. It offered to forgo further investigations in exchange for a one-time payment. Despite its amateurish appearance, this malware first emerged in 2011 and caused significant harm.


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