What is Computer Virus?

Introduction

A computer virus is a type of software program or a piece of code that when executed modifies other computer programs or other data resulting in either the spread of the infection or destroying of information. Some computer viruses need a host program to propagate, similar to their biological variant the virus infects the host, then the host when executed also executes the virus and the infection is spread to other files as well.

Computer viruses date way back to the early 1970s when the first virus known as the creeper virus was discovered in the ARPANET. To remove this computer virus another program was written known as Reaper. This program removed the creeper virus from the system. This program can be considered synonymous with antivirus programs available now. In the article, we will see how these computer virus work and their types, and how these viruses infect and spread. And lastly how to protect your computer from viruses.

Definition of Computer Viruses

A computer virus can be formally defined as a hidden, self-replicating computer program that contains malicious code which can infect a computer without the permission or knowledge of the user and might corrupt, steal and delete the data on the computer. It can use various available methods to spread such as infecting any removable media device on that computer or infecting files that are sent as attachments, etc.

A computer virus comprises three parts: the infection mechanism, the trigger, and the payload. The infection mechanism contains information about how the virus spreads. The virus can propagate in various ways such as infecting particular files based on the infection vector. The next part is the trigger, as mentioned above some virus needs a host to activate.

For example, whenever the infected file is executed, the malicious code is also triggered to run. And lastly is the payload which is the malicious code written by the attacker to perform the malicious actions.

Common Signs of Computer Viruses

Whenever your system is affected by computer viruses it might cause system failure, data corruption, wastage of computer resources (processing power is used for some other activity), and leakage of sensitive information. Following are some commonly observed signs of computer virus infection.

1. Speed of System :
   The most commonly observed sign of a computer virus infection is slowing down your system. As the virus introduces unwanted processes and tasks which keep running in the background utilizes the computer resources in turn slowing down the systems. Sometimes these viruses transfer data over the internet to the attacker, therefore, slowing down the internet speed too. Nowadays these crypto miner viruses utilize the resources of your system to mine cryptocurrency for the attacker.

2. Pop-up Windows :
   Another commonly seen sign of infection includes unwanted popups. Initially, these viruses caused popups either to lure the victim into performing some malicious action such as getting administrative privilege, or sometimes pop-up windows were just used to annoy the victim.

3. Programs Self-executing :
   If you notice that any program is executing or exiting without any input from the user and is not set up for auto start than most probably a virus is behind this behavior which has modified that particular software resulting in this erratic behavior

4. Accounts Being Logged Out :
   Sometimes the viruses lead to the crashing of applications leading to accounts being logged out. Or some viruses create a fake login page so that when the victim enters the credentials, these are sent to the attacker instead.

5. Crashing of the Device :
   These viruses can result in erratic system calls leading to a system crash and sometimes these viruses can remove important system files which cause the operating system to crash and be unable to boot back.

6. Mass Emails Being Sent from Your Email Account :
   Emails are one of the most commonly used attack vectors for these computer viruses. If an attacker gains access to a victim’s email account emails with malicious attachments are sent to the entire directory to spread the virus even further as people are more susceptible to downloading an attachment from a known person rather than someone unknown.

7. Changes to Your Homepage :
   This is also one of the most commonly observed side effects of a computer virus infection. The victim can observe that the browser's setting has been changed. Some new extensions are installed, the search engine is changed, the home page has been changed, etc. This means the browser has been impacted by a virus.

How Do Computer Viruses Attack and Spread?

Now that we know what is a computer virus, let us now see how these computer viruses attack. As discussed above a computer virus contains three parts that are the infection mechanism, the trigger, and the payload of the virus. The infection mechanism is responsible for the propagation of the virus and the infection of new files. The trigger is the logic used to start the execution of the malicious code of the virus.

For example, if the virus is attached to a file and the logic is set that whenever that particular file is being executed the virus also executes, another example would be a logic bomb which executes on a particular date, time, or any other specified condition. And the last part is the payload of the virus that contains the malicious code or instructions as to what would be the function of the virus. The execution of the payload can be considered a successful computer virus attack.

These computer viruses can spread and infect a variety of different subsystems on their host computers and software. Various ways can lead to the spreading of a computer virus which includes malicious attachments or links in phishing emails, trojan horses in pirated software, and the user falling victim to some sort of cyberattack and downloading viruses unknowingly. And the most common method of spread is through the use of infected removable memory devices.

Types of Computer Viruses

There are various types of computer viruses present that can be classified further based on their functionality that is how they affect the system and the other is based on their mode of transmission. Some of the prevalent computer viruses are :

1. Resident Virus :
   It is a kind of malicious software that hides and keeps itself stored in the computer's primary memory (RAM). Then, based on the virus's code, it can infect any file that the computer runs. This sort of virus can even integrate with anti-virus software, enabling it to infect any file that the program scans. Example – ‘Jerusalem Virus’.

2. Multipartite Virus :
   It is a particular kind of quick-acting malware that targets both executable files and the boot sector of a device at once. Because they have more dissemination options than conventional computer viruses. The multipartite virus is considered more harmful than other viruses as these attack computers more than once and at different times leading to the system being repeatedly getting infected. This virus also results in performance issues and memory crashes. Example – ‘Ghostball’.

3. Direct Action :
   It is a virus that particularly affects the .exe and the .com files. They usually infect and destroy all the executable files. Although this virus usually degrades a system's performance, it is also capable of wiping out all the data on a computer's hard drive and any USB devices that are connected to it. But at the same time, they are very simple to detect and their removal is easy too. Example – ‘Rugrat’.

4. Browser Hijacker :
   It is a kind of virus that meddles with the browser's proper functioning. This virus changes the search engine, changes the homepage, adds some unwanted extensions resulting in pop-ups and advertisements, and sometimes also leads to the leaking of sensitive information saved in the browser. Example – ‘CoolWebSearch’.

5. Overwrite Virus :
   As the name suggests this virus overwrites the data with dummy data resulting in the loss of important information. The infected files can further infect other files. The data infected cannot be brought back. Example – ‘Grog. 202/456’.

6. Web Scripting Virus :
   This virus also affects the web browsers and web pages the victims are using, it breaches the web browser's security to impede the normal functioning of the device, corrupt files, and steal sensitive information. It may look alike a browser hijacker virus but it is more enhanced and cause much more damage.

7. File Infector :
   In File infector virus as the name suggests generally the .exe and the .com files are infected by copying the code of the virus into the files and they spread fast. Example – ‘Cascade’.

8. Network Virus :
   The network virus is spread from one computer to another in a network through network packets and it does not require a file-based copy of the virus to spread rather it spread directly. It is hard to detect through anti-virus and a successful infection can lead to possible data theft, decreased performance, and network downtime.

9. Boot Sector Virus :
   The boot sector virus is the kind of virus that affects the boot sector of the machine. It infects the Master Boot Record (MBR) of the hard disk and it is loaded into primary memory each time the operating system boots up. They were mainly spread through infected removable media devices. Example – ‘Brain’.

How to Protect your Computer from Viruses?

With evolving technology, there is no foolproof plan or method to protect your computer from a computer virus. Although there are some precautions that we should always follow to prevent further damage in case of an attack and be able to prevent the majority of virus attacks.

The various ways to protect and prevent an attack include :

• Using antivirus software which prevents the majority of virus attacks as the antivirus companies keep updating the virus databases thus preventing any attack from newer variants of viruses.
• Not clicking any suspicious links and attachments sent over in the email. Always scan the email for possible viruses before opening them.
• Not downloading any pirated software, most of the time viruses are bundled with the free software and when the pirated software is installed the virus is also executed.
• Never click any pop-up advertisements, not only because they are fake but also, because they may lead to giving unwanted permissions to applications or viruses resulting in more loss.
• Always update all the software systems available to the latest versions available reducing the risk of possible attack vectors.