What is Malware? How Does It Work?

Personal computers, servers, mobile, and IoT devices have become an integral part of daily life. This situation has made cyber attackers’ attacks and attack methods quite diverse. Malware is also among the frequently used methods by cyber attackers. So, what are the types of malware, how do they work, and how do they spread? Let’s take a closer look.

What is Malware?

Cyber attackers have several different methods to gain access to a system. Malware, derived from the English words “malicious software,” is one of the most common methods used by hackers to infiltrate a system.

Malware is software that installs itself on a system without the user’s knowledge or consent, aiming to cause various damages. Malware can corrupt files on the computer, breach data security, disable the system, hold files hostage for ransom, or simply annoy users with spam advertisements.

What Are the Types of Malware?

Malware is categorized into various subtypes based on their purposes, working methods, and structures. Viruses that come along with files, worms that copy themselves from one computer to another, and trojans that secretly infiltrate computers are some of the malware types. Now, let’s take a closer look at the many kinds of malware.

Virus

Computer viruses are often used as a general term for all malware, but this usage is not entirely accurate. Computer viruses spread from one computer to another much like biological viruses spread from one living being to another. They perform specific functions to damage the infected system, usually by deleting files to sabotage the system.

Viruses attach themselves to executable files to run their code and spread from computer to computer. When a user opens a suspicious file, the virus activates. There are many types of viruses, such as file viruses, boot sector viruses, macro viruses, network viruses, companion viruses, logic bombs, cross-site scripting viruses, and DOS viruses.

Worm

Worms share similar characteristics with viruses and can be seen as a subclass of viruses. Worms spread by copying themselves from one computer to another. Worms work autonomously without any user interaction and can spread via email, websites, removable devices (USB drives, CDs). They can render memory and network bandwidth unusable and allow cyber attackers to run software in the background to access personal information.

Rootkits

When malware enters a system, it can be detected through security software or by monitoring system resource usage. Rootkits gain administrator privileges and hide themselves within the system. With admin rights, they can deceive detection software.

Rootkits’ hiding capabilities allow other malware to remain concealed within the system. Rootkits can hide backdoors created for system access, keyloggers that monitor keyboard usage, or turn the system into a zombie computer used for further cyberattacks. For example, the malware called Zacinlo, which spreads through fake VPN software, removes competing malware from the system and then secretly opens invisible web browsers in the background to generate fake ad clicks.

Backdoor

Imagine a system equipped with security software that monitors all inputs and outputs. Internet traffic and external drives are scanned for malware. A cyber attacker installs a backdoor in the system to bypass all these controls. This allows remote control over the computer.

Backdoors are installed on a system via another malware such as a virus or trojan. Backdoors can exist in installed software, operating systems, or hardware firmware. They may be purpose-built malware or vulnerabilities discovered in software that attackers exploit to gain access.

Trojan Horse

Named after the myth of the Trojan Horse used by Odysseus to infiltrate the city of Troy, trojan malware disguises itself as harmless software to trick users into installing it. They silently infect the system through seemingly innocent email attachments or downloaded software. Trojans can install cryptocurrency mining software, keyloggers, or backdoor programs on the system.

Ransomware

Ransomware locks access to files on the infected system and demands payment from users. Attackers encrypt files or disable the system and request a ransom to reverse the damage. Recently, ransomware attacks targeting companies and encrypting their data have become very common. Payments are usually demanded in cryptocurrencies, which are hard to trace.

Ransomware can be divided into four categories. Encrypting ransomware, as described above, encrypts files and demands a ransom key. Non-encrypting ransomware makes the system unusable by flooding it with images, notifications, or windows that cannot be closed. Leakware or doxware threatens to publish sensitive data stolen from the user’s system.

With the rise of mobile devices, mobile ransomware has emerged. Since mobile data is usually synced online or stored in the cloud, these malware tend to disable the device rather than encrypt data or use leakware methods.

The most well-known ransomware is CryptoLocker, which appeared in 2013. It infected computers and networks by encrypting files and demanding payment in Bitcoin within a specific time. Though CryptoLocker is no longer active, many imitators have emerged.

Adware

Adware is the least dangerous malware type that can infect a system. It uses user data to deliver targeted advertisements. Attackers can use it to display annoying ads frequently or show ads that can lead to further malware infections. Adware can also change the search engine and track web activity.

Spyware

Spyware is a common malware type that collects personal data and monitors the user’s activities without their knowledge. Unlike viruses and worms, spyware does not aim to copy itself but to hide and monitor users.

Spyware can target individuals or be used to steal commercial secrets.

Keylogger

Keyloggers record keystrokes on the infected system and send them to attackers. Every keystroke, including passwords and credit card details, is captured. They spread via emails, malicious websites, and pirated software.

Browser Hijacking

This malware installs with software or browser extensions and can change the browser’s homepage, show unwanted ads, collect browser data, or automatically open pop-ups that may download other malware.

Scareware

Scareware tricks users by showing fake warnings about malware on their system and tries to sell fake antivirus, security, or maintenance software by creating fear.

Botnets

Botnet malware turns your computer into a bot that follows attackers’ commands. Infected devices are organized and used for DDoS attacks, sending spam, and other purposes.

For example, Mirai malware discovered and enrolled IoT devices with ARC processors into a botnet network, launching a DDoS attack against the Minecraft game infrastructure in 2016.

Fileless Malware

As the name suggests, fileless malware does not store any files on the hard drive. It runs in the user’s memory, making it difficult for security software to detect.

For instance, Microsoft Defender ATP research team revealed that the Astaroth trojan spread using fileless malware via spam files with the .LNK extension. It settled in memory and then downloaded and ran a trojan.

How Do Malware Work? How Do They Spread?

Malware infects a clean system from outside. It can spread through email attachments, USB drives received from others, or when downloading fake or pirated software. Even with caution, security vulnerabilities in software can act as backdoors exploited by attackers.

Malware’s common trait is to secretly embed itself in the system and run unnoticed. Viruses and worms spread from one computer to another, while trojans aim to secretly infiltrate the system and then install other malware. Backdoors, keyloggers, and spyware aim to operate undetected for long periods.

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