Episode 111: Malware Types — Virus, Worms, Keyloggers, Rootkits

This episode dives into the various types of malicious software, or malware, that technicians must be able to recognize and address. We begin with viruses, which attach to legitimate files and require user interaction to spread, then move into worms, which self-replicate across networks and can bring down systems without any user action. We explain how these differ in propagation methods and damage potential, which is a frequent point of confusion on the exam.

Next, we discuss keyloggers—software or hardware tools that silently record keystrokes to capture sensitive data—and rootkits, which deeply embed themselves into the operating system to avoid detection and persist over time. Understanding the characteristics and behaviors of each malware type is essential for selecting the correct remediation strategy. These distinctions also help when analyzing exam questions about symptoms, threats, or attack vectors. Brought to you by BareMetalCyber.com.

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Understanding the different types of malware is essential for anyone working in technical support, system administration, or cybersecurity. Malware is a general term for any software intentionally designed to cause damage, steal data, or disrupt operations. Each type of malware behaves differently and requires a unique response. For this reason, the A Plus exam includes questions that ask you to identify the malware type based on symptoms or behavior. Recognizing these patterns helps technicians apply the right removal process, understand how a system was compromised, and prevent further infection.
A computer virus is one of the oldest and most well-known forms of malware. A virus attaches itself to a host file, such as an executable program or document. It requires user interaction to spread—usually by opening or running the infected file. Once active, a virus can corrupt data, damage system files, slow performance, or replicate itself to other files and systems through removable media or shared directories. Some viruses are harmless pranks, but others are destructive and can render a system unusable if not contained quickly.
Worms operate very differently from viruses. A worm is a self-replicating piece of malware that spreads without any user action. It often targets vulnerabilities in network protocols, file sharing services, or unpatched operating systems. Once inside a network, a worm can multiply rapidly, causing performance problems, system crashes, or bandwidth overload. Because worms spread so efficiently, they are frequently used in large-scale attacks designed to infect thousands or even millions of devices within a short period.
Trojans, also known as Trojan horses, are deceptive programs that appear to be legitimate software but contain hidden malicious functionality. A Trojan may disguise itself as a system utility, a game, or even an antivirus tool. When executed, the Trojan activates its payload, which could disable system protections, install additional malware, or create a backdoor for remote access. Unlike worms, Trojans do not spread on their own; they rely on user action for delivery. They are often sent as email attachments or downloaded from fake websites.
Keyloggers are a type of spyware designed to capture every keystroke typed on a keyboard. This allows attackers to steal sensitive information such as usernames, passwords, credit card numbers, and confidential messages. Keyloggers can be installed as software or embedded as physical devices connected between the keyboard and the computer. Software-based keyloggers run silently in the background and are difficult to detect without security tools. Because they record everything typed, they pose a significant risk to personal and corporate security.
Spyware operates in a similar fashion but is usually broader in scope. Instead of just recording keystrokes, spyware may track browsing history, monitor application usage, capture screenshots, or harvest contact lists. Some spyware is bundled with free software, browser extensions, or apps that promise convenience but deliver surveillance instead. Once installed, spyware can report user behavior back to the attacker continuously. It can also open up a system to additional threats by weakening security settings or disabling system updates.
Rootkits are among the most dangerous forms of malware because of their ability to remain hidden. A rootkit buries itself deep in the operating system—often at the kernel or driver level—and modifies system functions to avoid detection. Once installed, a rootkit can hide files, processes, and registry keys from both the user and antivirus software. This makes them extremely difficult to detect or remove. In many cases, the only effective response is to reformat the drive and reinstall the operating system from trusted media.
Adware is another form of potentially unwanted software that shows intrusive ads, pop-ups, or redirects. Some adware changes browser settings, injects ads into search results, or tracks user behavior for marketing purposes. While not always malicious in intent, adware consumes system resources and disrupts productivity. It often comes bundled with free downloads and is sometimes referred to as grayware when it blurs the line between legitimate advertising and unauthorized activity. Legitimate software may include adware with unclear disclosure, making it difficult for users to recognize the risk.
Ransomware is a high-profile threat that encrypts the user’s files and demands payment in exchange for a decryption key. This type of malware can enter through phishing emails, malicious downloads, or exploited vulnerabilities. Once activated, it locks the user out of their files and presents a ransom note, often demanding payment in cryptocurrency. Some variants also threaten to publish stolen data if the ransom is not paid. Ransomware has crippled hospitals, governments, and businesses, making it one of the most serious modern threats.
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Fileless malware represents a stealthy evolution in attack methods. Unlike traditional malware that writes executable files to disk, fileless malware operates entirely in system memory. It typically leverages trusted system utilities, such as PowerShell or Windows Management Instrumentation, to carry out its tasks. Because it leaves no files behind, signature-based antivirus tools often miss it. Detection depends on behavioral analysis that monitors suspicious patterns, like scripts running with elevated privileges or unexpected command execution. Fileless malware is particularly dangerous in environments that rely solely on traditional endpoint protection.
Botnets are another advanced malware construct. A botnet is a network of devices—often called zombies—that have been infected and brought under the control of an attacker. The user of an infected machine may be completely unaware that their system is participating in malicious activities. Botnets can be used to launch distributed denial-of-service attacks, send spam emails, harvest data, or mine cryptocurrency. They are controlled remotely through command and control channels, and the infections often remain dormant until activated by the attacker. Detection typically requires network monitoring to identify unusual traffic patterns.
Polymorphic and metamorphic malware are designed to evade detection by constantly changing their code. Polymorphic malware modifies parts of itself while retaining the original functionality, often altering its encryption keys or structure every time it spreads. Metamorphic malware takes this a step further by completely rewriting its code with each iteration, making it even harder to identify. These behaviors confuse signature-based scanners, which rely on identifying known code patterns. Behavioral and heuristic tools offer a better chance of detecting these advanced threats by focusing on what the malware does rather than how it looks.
Consider this real-world scenario. A user finds a flash drive in a parking lot and plugs it into their work computer. The flash drive contains an autorun worm that silently installs itself and begins scanning the local network for accessible shares. Once it finds unprotected folders, it copies itself and continues spreading. The infection is discovered after the help desk receives multiple complaints about sluggish systems and missing files. The response involves isolating the infected machines, cleaning them with endpoint protection tools, and deploying a policy to disable autorun features company-wide.
Recognizing the signs of malware infection is critical. Common symptoms include slow performance, unexpected pop-ups, or processes consuming large amounts of CPU or memory. Users may also notice missing files, unexplained network activity, or unauthorized login attempts. In extreme cases, entire systems may become unresponsive or display altered user interfaces. A single symptom is not definitive proof, but a pattern of behaviors should prompt further investigation using antivirus logs, task managers, and network analysis tools.
Zero-day malware refers to malicious code that exploits a vulnerability unknown to the vendor and unpatched in all existing systems. Because there is no fix available at the time of the attack, zero-day exploits are especially dangerous. They are often used in targeted campaigns against high-value organizations. Detection relies heavily on heuristic and behavioral analysis, as well as intrusion detection systems that look for unusual activity. Layered security practices, including regular software updates, access restrictions, and system monitoring, are the most effective defense against zero-day threats.
Malware often takes advantage of system vulnerabilities to increase its impact. This may include elevating privileges, disabling security features, or hiding its activity from monitoring tools. These weaknesses exist because of coding errors, poor configurations, or outdated software. The connection between vulnerabilities and malware is direct—patching systems not only fixes bugs but removes the entry points that malware depends on. Educating users about safe behavior also reduces the risk of accidental activation, such as clicking on a malicious link or running an untrusted file.
Many modern malware threats include multiple components in a single package. A Trojan may be designed to look like a legitimate tool but may install a keylogger, create a backdoor, and disable antivirus all at once. This layered approach allows attackers to maintain access, gather information, and carry out multiple objectives simultaneously. Malware with multiple payloads is more complex to detect and remove, because it may react to scanning or cleaning attempts by changing tactics or reinstalling itself from hidden components.
There are several tools available to help identify and classify malware. Antivirus logs provide detection reports and quarantine actions. Task Manager may reveal unknown or suspicious processes, especially those consuming abnormal resources. Network monitoring tools can highlight unusual outbound connections or excessive bandwidth usage. More advanced environments use sandboxing, which isolates and runs a suspected file in a controlled environment to observe its behavior. Event logs and security auditing tools may also uncover evidence of unauthorized access or failed login attempts associated with malware activity.
To summarize, understanding malware means more than recognizing a few buzzwords. You must know how viruses, worms, Trojans, spyware, ransomware, and rootkits operate, how they spread, and what signs they leave behind. Newer forms like fileless malware, polymorphic code, and botnets introduce new challenges for detection and response. With the right knowledge, technicians can identify threats early, apply the proper tools, and help protect systems from further harm. The A Plus exam tests these concepts regularly through scenarios and symptom-based questions.