Definition of computer viruses, how they work, how they spread, and their types?

When we talk about computer security, viruses are the primary threat that poses a danger to computers, capable of destroying a single program or the entire computer system.

What are viruses?

A virus is a malicious software downloaded onto a user's computer without their knowledge, executing harmful actions. The virus replicates itself by copying into other programs, spreading to executable documents or files. Its purpose is to infect computer systems, take control of them, and steal users' private data.

The first virus, named Creeper, was created in the 1970s, and in 1981, the first virus spread through Apple-produced floppy drives.

According to the Information Technology Promotion Agency, the number of viruses rose to 52,151 in 2004. With the use of antivirus software, this number decreased to around 14,000 in 2010.

How does a virus work?

A virus operates in two ways:

The first type begins working and replicating as soon as it reaches a new computer.

The second type remains dormant until the user runs the infected program, at which point it activates.

Recently, advanced viruses have emerged with high capabilities to evade antivirus programs and other advanced defense levels. Their evolution allows them to dynamically alter their code, making virus detection and identification extremely challenging.

How does a virus spread?

One of the ideal methods for virus spread is through email messages by opening attachments, links, visiting infected websites, clicking executable file links, or viewing untrustworthy ads. Viruses can also spread via removable storage devices like USB flash drives that carry the virus.

Types of Viruses:

There are various types of viruses based on the functions they are designed to perform. It's essential to be aware of the kinds of viruses that affect our computers:

1. Resident Virus:

        Residing in the computer's Random Access Memory (RAM), this virus can interfere with regular system operations, leading to file and program corruption. Common examples include CMJ, Meve, MrKlunky, and Randex.

2. Multipartite Virus:

        Easily spreads throughout the computer system, these viruses are highly dangerous, causing unauthorized actions in the operating system, folders, and other computer programs.

3. Direct Action Virus:

        Attacks specific file types like .exe and .com. These viruses primarily aim to replicate and infect files in folders without typically deleting files or affecting computer performance. They can be easily removed by antivirus programs.

4. Browser Hijacker:

        Infects web browsers, redirecting users to multiple different sites. When a user enters a search query, the virus opens various fake websites harmful to the computer. Trusted browsers often have built-in features to directly block these viruses.

5. Overwrite Virus:

        Writes over the content of files, leading to the loss of the original content. This type affects folders, files, and even programs. Removing this virus requires identifying the infected file and eliminating it, emphasizing the importance of backing up intact data.

6. Web Scripting Virus:

        Comes from certain links, ads, image sites, or videos containing malicious code. These viruses automatically download when visiting malicious websites or interacting with harmful content.

7. Companion Virus:

        This virus type needs an attached file or folder to cause damage. The associated file must be opened for the virus to activate, as seen in examples like Terrax.1069, Stator, and Asimov.1539.

8. Network Virus:

        Spreads across Local Area Networks (LANs) and the internet, proliferating through shared resources like drives and folders. Network viruses search for potential victims when entering a computer, exemplified by Nimda and SQLSlammer.

For Other Malware:

Other threats aren't specifically called viruses, but they have similar detrimental effects. This includes worms, adware, and ransomware.

To prevent these viruses from impacting your computer, it's important to install antivirus software capable of detecting, blocking, and eliminating all types of computer viruses.