Virus
A computer virus is a type of malicious software designed to self-replicate and spread to other computers. Viruses can modify or destroy data, disrupt computer systems, and utilize system resources without user consent.
TL;DR — what is a computer virus and how does it differ from malware?
Computer virus — what is it? A computer virus is a type of malicious software capable of self-replication: it attaches itself to files or programs and spreads to further computers, modifying data or disrupting how systems work. To become active it needs a host, meaning an infected file, and an action by the user, such as opening an attachment or running a program.
Beware of a common shortcut: a “virus” is only one category of malware, a broader term that also covers worms, trojans, ransomware and spyware (a virus needs a host and user action, while a worm spreads on its own). Infection symptoms include slowdowns, crashes and unusual activity. Protection: up-to-date antivirus/EDR, regular updates, caution with attachments and backups.
nFlo protects company workstations, laptops and servers against viruses and other malware through its Managed EDR/XDR service: analysts manage the EDR/XDR platform (CrowdStrike or SentinelOne) around the clock, triage alerts, run threat hunting, isolate compromised hosts and respond to incidents.
Computer Virus Definition
Computer virus is a type of malicious software designed to self-replicate and spread to other computers. Computer viruses can modify or destroy data, disrupt computer system operations, and utilize system resources without user consent.
How Does a Computer Virus Work?
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Infection: The virus enters the computer system through infected files, programs, email attachments, or removable media.
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Replication: The virus copies itself and spreads to other files, programs, or systems.
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Activation: The virus may be activated by a specific event, such as running an infected file.
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Action: The virus performs its malicious actions, such as deleting files, stealing data, or disrupting system operation.
What Are the Types of Computer Viruses?
The simplest way to group computer viruses is by what runs them. NIST (SP 800-83) distinguishes two groups: compiled viruses, executed by the operating system, and interpreted viruses, executed by an application. The first group includes file infectors, boot sector viruses and multipartite viruses; the second — macro viruses and scripting viruses. Below are the most common kinds and types of computer viruses:
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File Viruses: Infect executable files (.exe, .com) and run along with them.
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Boot Sector Viruses: Attack the boot sector of a hard drive or removable media.
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Multipartite (Hybrid) Viruses: Combine the traits of a file infector and a boot sector virus, so they can infect both programs and the disk’s start-up area.
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Macro Viruses: Infect documents and files containing macros, such as Microsoft Office files. Microsoft blocks VBA macros in files from the internet by default in Office apps, which narrows this infection route without closing it — a user or administrator can lift the block.
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Scripting Viruses: Infect scripts executed by scripting languages that services on the operating system process.
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Polymorphic Viruses: Change their code with each infection to avoid detection by antivirus software.
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Resident Viruses: Embed themselves in computer memory and infect files while they are being used.
Virus Spreading Methods
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Email Attachments: Viruses can be sent as attachments to email messages.
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Infected Files: Downloading and running infected files from the internet.
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Removable Media: Transferring viruses via media such as USB drives, hard drives, and CD/DVDs.
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Security Vulnerabilities: Exploiting vulnerabilities in operating systems and applications.
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Computer Networks: Spreading viruses through local networks and the internet.
Virus Infection Symptoms
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System Slowdown: Unusual drops in computer performance.
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Unexpected Messages: Appearance of unknown messages or windows.
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File Changes: Unexpected changes or deletion of files.
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Startup Problems: Difficulties starting the operating system or applications.
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Unusual Network Activity: Increased network traffic without apparent reason.
Virus Impact
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Data Loss: Deletion or corruption of important files and data.
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Information Theft: Theft of confidential data such as passwords and credit card numbers.
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System Disruption: Disruption or complete prevention of operating system operation.
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Resource Exploitation: Using system resources for DDoS attacks or cryptocurrency mining.
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Repair Costs: Costs associated with removing viruses and restoring systems to normal operation.
How to Detect a Virus on Your Computer?
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Antivirus Software: Using up-to-date antivirus software to scan and detect viruses.
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System Monitoring: Tracking unusual system activity, such as slowdowns and unexpected messages.
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File Scanning: Regular scanning of files and removable media.
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System Updates: Regular updates to the operating system and applications to eliminate security vulnerabilities.
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Log Analysis: Reviewing system and network logs to detect suspicious activity.
Virus Protection Methods
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Antivirus Software: Installing and regularly updating antivirus software.
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Software Updates: Regular updates to the operating system and applications.
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Safe Browsing: Avoiding suspicious websites and links.
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Download Caution: Downloading software only from trusted sources.
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Attachment Scanning: Scanning email attachments before opening.
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Backups: Regular backups of important data.
Differences Between Viruses and Other Types of Malware
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Virus: Self-replicating malware that requires user interaction to spread.
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Worm: Self-replicating malware that spreads autonomously through networks. Unlike a virus, it is a standalone program and needs neither a host nor a click — details in the article What is a computer worm.
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Trojan: Malware that masquerades as legitimate applications to gain system access. Unlike a virus, it does not replicate — see the trojan entry.
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Ransomware: Malware that encrypts data and demands ransom for decryption.
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Spyware: Software that collects user data without their knowledge.
Related Terms
- Malware - broader category of malicious software
- Trojan - malware masquerading as legitimate programs
- Ransomware - malware that encrypts data
- EDR - detecting and responding to viruses
Explore Our Services
Want to protect your organization against viruses? Check out:
- SOC 24/7 - monitoring and virus detection
- Incident Response - infection removal
- Security Awareness Training - employee education
Computer viruses are a serious threat to computer and data security. It’s important to be aware of how viruses work and apply appropriate protection measures to prevent infections and minimize risk.
Frequently asked questions
+ What is a computer virus?
A computer virus is a malicious program that copies itself by inserting its code into other programs or files and in this way spreads to further computers. According to NIST, a virus cannot run on its own: it becomes active only when its host program is run. It can destroy or modify data, steal information and slow down the system.
+ How does a computer virus work?
A virus reaches a system inside an infected file, program, email attachment or removable media. Once the host is run, it copies itself into further files or programs and, when a given condition is met, carries out its payload, for example deleting files, stealing data or disrupting the system. This is why updates and caution with attachments matter so much.
+ What are the types of computer viruses?
The most commonly listed types are file viruses that infect executable files, boot sector viruses that attack the start-up area of a disk, macro viruses in documents with macros such as Microsoft Office files, polymorphic viruses that change their code to avoid detection, and resident viruses that embed themselves in the computer's memory.
+ How is a computer virus different from a worm?
A virus copies itself by inserting its code into other programs or files and usually needs a user action, such as opening a file. A worm is a standalone program that replicates and typically runs itself without human involvement — most often through a vulnerability in a network service or as a mass-mailing worm. That is why a worm can infect many computers on a company network in a short time.
+ Is an "internet virus" the same as a computer virus?
Not always. Strictly speaking, a virus is malicious code that replicates by inserting itself into other files or programs. The term "internet virus" is often used loosely for any malicious software that reaches a computer over the network — including worms, trojans and spyware. All these categories fall under the broader term malware.