Computer Viruses Meaning, Types & Prevention

31/07/2022 0 By indiafreenotes

A computer virus is a type of computer program that, when executed, replicates itself by modifying other computer programs and inserting its own code. If this replication succeeds, the affected areas are then said to be “infected” with a computer virus, a metaphor derived from biological viruses.

Computer viruses generally require a host program. The virus writes its own code into the host program. When the program runs, the written virus program is executed first, causing infection and damage. A computer worm does not need a host program, as it is an independent program or code chunk. Therefore, it is not restricted by the host program, but can run independently and actively carry out attacks.

Virus writers use social engineering deceptions and exploit detailed knowledge of security vulnerabilities to initially infect systems and to spread the virus. Viruses use complex anti-detection/stealth strategies to evade antivirus software. Motives for creating viruses can include seeking profit (e.g., with ransomware), desire to send a political message, personal amusement, to demonstrate that a vulnerability exists in software, for sabotage and denial of service, or simply because they wish to explore cybersecurity issues, artificial life and evolutionary algorithms.

Computer viruses cause billions of dollars’ worth of economic damage each year.

In response, an industry of antivirus software has cropped up, selling or freely distributing virus protection to users of various operating systems.

The terms “Virus” and “malware” are often used interchangeably, but they’re not the same thing. While a computer virus is a type of malware, not all malware are computer viruses.

The easiest way to differentiate computer viruses from other forms of malware is to think about viruses in biological terms. Take the flu virus, for example. The flu requires some kind of interaction between two people like a hand shake, a kiss, or touching something an infected person touched. Once the flu virus gets inside a person’s system it attaches to healthy human cells, using those cells to create more viral cells.

A computer virus works in much the same way:

  • A computer virus requires a host program.
  • A computer virus requires user action to transmit from one system to another.
  • A computer virus attaches bits of its own malicious code to other files or replaces files outright with copies of itself.

It’s that second virus trait that tends to confuse people. Viruses can’t spread without some sort of action from a user, like opening up an infected Word document. Worms, on the other hand, are able to spread across systems and networks on their own, making them much more prevalent and dangerous.


There are several types of computer viruses that can infect devices. This section will cover computer virus protections and how to get rid of computer viruses.

Multipartite Virus

A multipartite virus uses multiple methods to infect and spread across computers. It will typically remain in the computer’s memory to infect the hard disk, then spread through and infect more drives by altering the content of applications. This results in performance lag and application memory running low.

Resident Virus

Viruses propagate themselves by infecting applications on a host computer. A resident virus achieves this by infecting applications as they are opened by a user. A non-resident virus is capable of infecting executable files when programs are not running.

Multipartite viruses can be avoided by not opening attachments from untrusted sources and by installing trusted antivirus software. It can also be prevented by cleaning the boot sector and the computer’s entire disk.

Direct Action

A direct action virus accesses a computer’s main memory and infects all programs, files, and folders located in the autoexec.bat path, before deleting itself. This virus typically alters the performance of a system but is capable of destroying all data on the computer’s hard disk and any USB device attached to it. Direct action viruses can be avoided through the use of antivirus scanners. They are easy to detect, as is restoring infected files.

Overwrite Virus

Overwrite viruses are extremely dangerous. They can delete data and replace it with their own file content or code. Once files get infected, they cannot be replaced, and the virus can affect Windows, DOS, Linux, and Apple systems. The only way this virus can be removed is by deleting all of the files it has infected, which could be devastating. The best way to protect against the overwrite virus is to use a trusted antivirus solution and keep it updated.

Browser Hijacker

A browser hijacker manually changes the settings of web browsers, such as replacing the homepage, editing the new tab page, and changing the default search engine. Technically, it is not a virus because it cannot infect files but can be hugely damaging to computer users, who often will not  be able to restore their homepage or search engine. It can also contain adware that causes unwanted pop-ups and advertisements.

Browser hijackers typically attach to free software and malicious applications from unverified websites or app stores, so only use trusted software and reliable antivirus software.

File Infector

A file infector is one of the most common computer viruses. It overwrites files when they are opened and can quickly spread across systems and networks. It largely affects files with .exe or .com extensions. The best way to avoid file infector viruses is to only download official software and deploy an antivirus solution.

Web Scripting Virus

A web scripting virus attacks web browser security, enabling a hacker to inject web-pages with malicious code, or client-side scripting. This allows cyber criminals to attack major websites, such as social networking sites, email providers, and any site that enables user input or reviews. Attackers can use the virus to send spam, commit fraudulent activity, and damage server files.

Protecting against web scripting is reliant on deploying real-time web browser protection software, using cookie security, disabling scripts, and using malicious software removal tools.

Network Virus

Network viruses are extremely dangerous because they can completely cripple entire computer networks. They are often difficult to discover, as the virus could be hidden within any computer on an infected network. These viruses can easily replicate and spread by using the internet to transfer to devices connected to the network. Trusted, robust antivirus solutions and advanced firewalls are crucial to protecting against network viruses.

Boot Sector Virus

A boot sector virus targets a computer’s master boot record (MBR). The virus injects its code into a hard disk’s partition table, then moves into the main memory when a computer restarts. The presence of the virus is signified by boot-up problems, poor system performance, and the hard disk becoming unable to locate. Most modern computers come with boot sector safeguards that restrict the potential of this type of virus.


There’s no way to stop viruses from being created. There will always be a young programmer wanting to prove that they can “Play with the big boys,” or a hacker who wants to just see chaos and damage. And, just like real-world vandalism, someone who creates viruses can start their “career” with a harmless prank but grow into causing millions of dollars of damage by deleting massive files from multiple corporations.

The best way to protect home computers against viruses is to have updated antivirus software, keep computers and software updated with the latest patches, and monitor the behavior of all users of a computer, including learning what types of files can be harboring viruses (such as Microsoft word documents in a massively forwarded e-mail). There will always be viruses, but staying vigilant will help keep a computer from becoming infected.

  1. Install antivirus or anti-malware software

It might seem obvious, but many home computers don’t have this protection. It’s essential to keep your PC virus free.

  1. Keep your antivirus software up to date

Protective software is one thing; but keeping it up to date is another. While free antivirus software is better than nothing, it’s not the best solution. Microsoft has a free security package if you operate with Windows, even though you would’ve already paid for the Windows licence. Many people don’t know about it; but, actually, it’s a good form of protection.

  1. Run antivirus scans regularly

This might also go without saying, but we often forget to do it. Adjust the settings so scans run at regular intervals (like once a week). Using the device while antivirus software is running can be challenging. Try running it at night when the computer is idle. Because we usually turn our devices off at night, we tend to overlook scans. Set the antivirus software to run on a specific night and only leave the computer on at that time. Make sure it doesn’t switch off automatically or go into hibernation mode.

  1. Keep your operating system up to date

Whether you use Windows, Mac OS X, Linux or another operating system, always keep it up to date. Developers regularly release patches to plug security leaks. The patches will help keep your system safe. You should also keep your antivirus software up to date. New viruses and malware are emerging constantly. Their software scanning is as sophisticated as their databases, so make sure you’re on top of things.

  1. Protect your network

Many PCs connect to files, printers and the Internet via Wi-Fi.  Make sure the network requires a secure password and never browse on open networks.

Use WPA or WPA2 encryption. PME is no longer secure enough. Expert hackers can circumvent it in minutes. It’s also a good idea not to disclose the name of your Wi-Fi network (the SSID). You can connect to the network manually on your device by typing in the SSID and password. If you usually let guests use your Internet, give them an alternative SSID and password just in case.

  1. Think before you click

Avoid websites you don’t trust. Don’t open email attachments from people or companies you don’t know. Don’t click on links in unwanted emails. Always hover the mouse over a link (especially a short URL) before clicking on it to see where it will take you.

If you need to download something from the Internet, an email, an FTP site, a file exchange service, etc., check it over first. Good antivirus software will do it automatically, although you have to make sure it’s running.

  1. Keep your personal information secure

This is probably the hardest thing to do on the Internet. Many hackers use social engineering over brute force to access your files. They can gather enough information to hack your online accounts to collect even more data.

They go from account to account until they have all they need to get hold of your bank details and steal your identity. Be careful on message boards and social media. Block all your privacy settings and avoid using your real name in chat forums.

  1. Don’t use unsecured Wi-Fi

Don’t use the free, open Wi-Fi (no password or encryption) in cafés, libraries, airports, etc. Think about it. If you can connect easily, how far can a hacker go?

  1. Back up your files

Backing up all your files is the best form of protection. Ideally, keep your files in three places: where you work on them (your computer); an external storage device; and somewhere else.

Use a back-up service or get two external hard drives and keep one at work; a relative or a friend’s house; or in a safe.

  1. Use several secure passwords

Never use the same password twice, especially for bank accounts. We usually use the same email address or username, which are easy to see and steal. If you always use the same password and someone uncovers it, it’ll take just a few seconds to hack into all your accounts.  Choose a strong password with lower- and upper-case letters, numbers and symbols. Make it easy to remember but difficult to predict. Don’t use dates or pets’ names.