Computer virus types, symptoms, protection and prevention

A computer virus is a type of malware designed to spread from computer to computer and perform harmful activities such as corrupting and disrupting systems or destroying data.

Types of computer viruses

Memory Resident Virus stays in memory after it executes and after its host program is terminated. In contrast, non-memory-resident viruses only are activated when an infected application runs.

Overwriting Virus will copy its code over the host computer system's file data, which destroys the original program.

Direct Action Virus is considered to be “non-resident” and functions by selecting one or more files to infect each time the code is executed. The primary intentions of this virus is copying itself and to spread infection whenever the code is executed.

Boot Sector Virus infects computer systems by copying code either to the boot sector on a floppy disk or the partition table on a hard drive. During startup, the virus is loaded into memory. Once in memory, the virus will infect any non-infected disks accessed by the system.

Cluster Virus associates itself with the execution of programs by modifying directory table entries to ensure the virus itself will start when any program on the computer system is started. If infected by this virus it will look like every program on your PC is infected; however, this virus is only in one place on the system.

Macro Virus is written in a macro language and infects Microsoft Word or similar applications (e.g., word processors and spreadsheet applications) and causes a sequence of actions to be performed automatically when the application is started or something else triggers it.

Polymorphic virus changes its code each time an infected file is executed. It does this to evade antivirus programs.

Multipartite virus infects and spreads in multiple ways. It can infect both program files and system sectors.

File infector virus inserts malicious code into executable files that are used to perform certain functions or operations on a system.

Web scripting virus exploits the code of web browsers and web pages. If you visit an infected web page, the virus can infect your computer.

Browser hijacker modifies a web browser's settings without a user's permission. It can inject unwanted ads into a web browser, replace the home page, error page, or search engine.

Symptoms of a computer virus

How to protect against a computer virus

The BEST antivirus is YOU.


You can have the best antivirus software on your computer, but even the best antivirus software can fail to detect new computer viruses and other types of malware.

Malware threats have grown significantly in the past decade. And these threats grow so fast that antivirus software take too long to catch up with malware (even the best programs).

Therefore, the best protection is yourself.

Educate yourself about malware and other cyber threats. Get some basic understanding, and you'll be much safer online and offline.

There's no better protection against computer viruses and other types of malware than yourself, so pay attention to everything you do, online and offline.

Always use antivirus software on your computer – even when antivirus programs can't protect you 100% against all malware.


It's better to have some protection than no protection at all.


Antivirus software can protect you against most known malware.

You should always install and use only one antivirus program on your computer.

Using multiple antivirus programs on a PC is a bad idea! Because:

There are so many free and paid antivirus programs out there that it's sometimes hard to choose one.

A good free antivirus is Microsoft Defender (formerly known as Windows Defender).

Microsoft Defender is already built-into Windows 10 and 11.

Microsoft Defender and common sense offer enough protection against most types of malware.

Another option is Bitdefender Antivirus Free.

If you need more functions (e.g., multi-layer ransomware protection) and settings, then you can try a paid antivirus program.

Many antivirus companies offer a free 30-day trial.

Two good paid antivirus programs are Bitdefender Antivirus and ESET Antivirus.

You can also use second opinion malware scanners to scan your computer for malware. You can use malware scanners to scan your computer for malware periodically (e.g., once a week) or when you think your computer is infected. You can use second opinion malware scanners alongside your current antivirus software without any problems.

A few good malware scanners are Kaspersky Virus Removal Tool, ESET Online Scanner, and Emsisoft Emergency Kit.

Other options are Malwarebytes and Norton Power Eraser.

If you're using GNU/Linux as an operating system and your day-to-day security practices are good, and your operating system is up-to-date, you don't need an antivirus because Linux malware is still rare at the moment.

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