What Is Malware? What Are Its Types?

Derived from the English term malicious software, malware—or in Turkish, zararlı yazılım—is the general name for software designed to damage or exploit any computer, phone, programmable device, service, or network. Malware is still one of the most popular weapons of cybercriminals, and it is essential to be extremely vigilant against it both in personal use and in enterprises. Let’s take a closer look at the answers to the questions what is malware, what are its types, and what measures can be taken to protect against such software!

The question what is malware can briefly be answered as: “malicious software.” The purpose of malware generally includes damaging devices, stealing confidential information, or using the device for malicious purposes without the user noticing. With different types of malware, cybercriminals can corrupt system files, slow systems down, or render them completely inoperable. They can also steal sensitive data such as credit card details, passwords, and personal information, and make the device remotely controllable.

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The most common types of malware include:

Viruses

Among common malware types, viruses are defined as program fragments that attach to other files and replicate when executed. Viruses most frequently spread through file sharing, removable media, email attachments, or malicious downloads. For example, when a user opens a file, the device can become infected. The goals of viruses include corrupting files, downloading additional malware, and degrading performance. If your device is infected, symptoms may include unexpected application crashes, slowdowns, and corrupted files. For protection against viruses in both individual and corporate environments, the primary measures are using reputable antivirus software and, of course, not opening suspicious attachments.

Worms

These are standalone programs that can self-replicate across networks without needing to attach to a file. Worms spread via open ports, vulnerable services, email attachments, or network shares. A sudden spike in network usage and the same issues occurring across multiple devices may indicate the presence of worm malware. Protection against worms includes network segmentation, security patching, IDS/IPS, and firewall solutions.

Trojan

As an example of malware, the Trojan (virus)—known in Turkish as “Truva atı”—is a type of software hidden within an application that appears benign but opens a backdoor or enables other malicious functions when executed. It typically spreads through social engineering, fake applications, and cracked software. With this malware, cybercriminals aim for remote access (RAT), data theft, and downloading additional malware. Indicators may include unknown network connections, remote access events, and unexpected new services. To protect against the Trojan malware, pay close attention to download sources and implement application whitelisting (beyaz listeleme).

Ransomware

Ransomware is a type of software that encrypts files, blocks access, and demands payment for decryption. It spreads via email attachments, malicious links, exposed RDP/services, and the supply chain. With this malware, cybercriminals seek data encryption, operational disruption, and ransom payments. Changes in file extensions, ransom notes, and mass encryption are key indicators of ransomware. Protection measures include regular backups, email filtering, access restrictions, and patch management.

Spyware

This type of software collects a user’s activities, browsing history, or sensitive data in the background. It spreads through add-ons, freeware, and malicious downloads. The goals of spyware include data collection, ad targeting, and identity theft. Indicators include changes in browser behavior and an increase in advertisements. Protection against spyware involves checking browser extensions and using privacy-focused AV products.

Adware

One of the frequently encountered malware types, adware displays persistent unwanted ads or alters browser behavior. Adware spreads through freeware and aims to generate revenue and track user behavior. Unwanted pop-ups and homepage/search engine changes may indicate exposure. Running scans for PUPs (Potentially Unwanted Programs) is important for protection.

Fileless Malware

This type of malware leaves no file on disk, runs in memory, and often leverages legitimate operating system tools. Fileless malware spreads via macros and phishing, and its goal is data exfiltration. Unusual use of legitimate tools and memory-based anomalies are common indicators. Protection measures include EDR/behavioral detection, script restrictions, and application whitelisting (beyaz listeleme).

Rootkit

This type of software embeds itself in deep layers of the operating system to hide itself and other malware. It spreads via system exploits and Trojans. The goal is long-term persistence without detection. Indicators include security software failing to run and abnormal kernel behavior. Protection requires secure boot and kernel-level safeguards.

Backdoor

A hidden entry point that enables unauthorized re-access to a system. It may be left behind after system compromise via Trojans/worms. The goal is remote command and control and data exfiltration. Common indicators include unknown services and unexpected outbound connections. Protection requires network monitoring, application whitelisting, and strong authentication policies.

And More…

In addition to the commonly known ones, other types of malware include:

• Keylogger: Software that records keystrokes and transmits them to the attacker.
• Botnet: A network of devices remotely controlled for malicious tasks, managed by a command-and-control server; also known as a zombie network.
• Macro Malware: Malicious commands hidden inside Office (Word/Excel) macros.
• Bootkit: Advanced malware that targets the boot process to gain control before the operating system loads.
• Dropper/Downloader: Small programs used to download/execute the main payload for the initial objective.
• Polymorphic/Metamorphic Malware: Malware that continuously changes (polymorphic) or rewrites (metamorphic) its code to evade signature-based detection.
• Mobile Malware: Trojans targeting smartphones, SMS Trojans, banking Trojans, and spyware apps.
• Potentially Unwanted Programs: May not be technically malicious but perform unauthorized behaviors (toolbars, add-ons). They often come bundled with software packages.

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