Computer viruses are unwelcome software programmes or fragments of code that infiltrate a computer’s operating system and cause it to malfunction. They spread by tainted files, data, and unprotected networks, among other methods. Once it has gained access to your system, it has the ability to duplicate and propagate from one software to another, as well as from one infected computer to another computer. Consequently, we may conclude that it is a self-replicating computer programme that interferes with the operation of the computer by infecting files, data and other software applications.
There are several antivirus applications available, which are programmes that can assist you in protecting your computer from infections. It examines your computer and removes any viruses that are discovered during the scan. Avast, Quickheal, McAfee, Kaspersky, and more well-known antivirus programmes are available for download.
Computer Viruses are classified into the following categories:
Virus that overwrites data:
It is the most basic type of computer virus, in that it simply overwrites the code of a file on the host computer system with its own destructive code. A portion or all of the content of the infected file is replaced with new material, without affecting the overall size of the file. As a result, it completely ruins the original programme code by overwriting it with the flawed code that it generated. Because this virus cannot be eradicated or cleaned, it is necessary to delete or replace the infected files with a fresh copy.
Virus that is appended to the end of a file:
In keeping with its name, this virus appends its harmful code to the end of the file containing the host software. After that, it modifies the file’s header in such a manner that the file’s header is redirected to the beginning of the harmful code contained within the add virus’ malicious code. As a result, this code is executed every time the application is launched. However, it does not completely destroy the host software; rather, it alters it in such a manner that it contains the viral code and allows the virus code to execute on its own.
A macrovirus is a virus that is larger than a virus.
A macro virus is a computer virus that modifies or infects the macros in a document or data file. It is included in a document as a macro and adds its codes to the macros already present in the document. When infected documents or data files are accessed in other computers, the virus spreads throughout the network.
It may also spread through software programmes that run macros, such as Microsoft Word and Microsoft Excel. Each time one of these apps is used to open a document, the virus spreads to additional documents that are tied to the original document.
The first macro virus, which was given the name idea, propagated through emails that contained Microsoft Word documents as attachments. This virus attacked Microsoft Word 6.0 and Microsoft Word 95 documents that had been saved using the Save As feature. Because of this, it did no damage other than to display an error message on the computer’s display screen.
Boot Virus (Boot Virus):
A boot virus, sometimes known as a boot sector virus, is a computer virus that affects the boot sector software contained on a computer’s hard drive or any other storage device, such as floppy discs. It causes the boot sector programme to be replaced with a malicious version of itself. Infecting the machine only occurs during the first boot-up process of the computer. If it accesses the computer after the boot-up procedure has completed, it will not infect it. Example: If someone forgets to remove the infected floppy disc from the computer before turning it on, the computer will boot into the infected boot sector software, which will then execute during the booting process. Example:
Typically, malware accesses your system through corrupted media files, malicious storage devices, and unprotected computer networks, among other methods. Because of the reduction in the usage of floppy discs and the widespread use of boot-sector protections in modern operating systems, the dissemination of this virus has become extremely rare in recent years.
Resident Viruses (RVs):
The virus that is resident in the computer’s primary memory (RAM) remains in the computer indefinitely. When you turn on your computer, it becomes active and begins to damage the data and applications that are already operating on it.
Viruses that are not resident in the host:
The non-resident virus, in contrast to the resident virus, does not take up residence in the computer’s memory. As a result, it is not run from the computer’s main memory. For example, viruses that are executable.
Virus with many parts:
A multipartite virus is one that distributes and infects in a variety of ways. It infects the boot sector of the computer as well as the executable files stored on the hard drive at the same time. When you switch on a computer, the boot sector virus is activated because it hooks on to the hard drive, which contains the data necessary for the machine to boot and operate. Once it has been activated, the software files get infected as well.
Virus that infects files: File Infector Virus
It is one of the most prevalent types of computer viruses that may be detected. Infecting executable files, such as those with the.com or.exe extensions, is the primary method of infection. When the virus-infected file is opened and run, the virus becomes active. The active virus overwrites a portion of the file or totally overwrites it. As a result, it has the potential to partially or entirely corrupt the original file.
Worm on the Computer:
A computer worm is similar to a virus, however it differs in that it is not a virus in the traditional sense. It has the ability to replicate and spread like a virus, but unlike viruses, it does not require the involvement of a host software in order to propagate. It has the ability to self-replicate, which means it can create many copies of itself. Infected computer systems are infected by computer worms that propagate over networks. For example, an email sent to an infected email address might infect your computer system.
Trojan Horse (also known as a ruse):
Trojan horse is a kind of malware that is similar to viruses and worms, although it is technically distinct from both. It does not have the ability to proliferate like a virus or a worm. A Trojan horse is a programme that disguises itself as another programme. Once you have installed any such application, the trojan horse will be able to infiltrate your computer system. It has the capability of granting illegal access to your computer, sending your data to other computers, deleting files, and doing other undesirable alterations to your computer system.
Cavity virus is a virus that affects the cavitation of the teeth.
The virus is also referred to as a “spacefiller virus.” As the name implies, this virus has a propensity to infiltrate a computer by occupying the vacant areas of a file. This virus is difficult to detect since it fills up the blank spaces in the file without altering the file’s overall size.
CMOS Virus (Chip Memory Virus):
It infects the CMOS chip, which stands for complementary metal-oxide semiconductor and is a memory chip that stores the configuration of the computer’s system. This virus has the capability of erasing or resetting the system settings.
Companion Viruses are viruses that travel with you.
It stores itself in a file with a name that is similar to the name of another programme file that is ordinarily run by the computer. When the application file is launched, the virus is activated and begins doing destructive actions on your computer’s hard drive, such as removing data from your computer’s hard drive. The Globe virus was the first known companion virus, and it was discovered in 1992 by researchers.
Virus with Encryption:
It encrypts its payload in order to make it more difficult to track down. After being downloaded, it is divided into two parts: the viral body and the decryptor, which decrypts the virus when it is performed. Following decryption, the virus is able to execute itself in order to proliferate and establish a permanent residence. Moreover, it differs from cryptolocker, which is a computer virus that encrypts hard drive data and keeps it hostage in exchange for a ransom payment.
Virus that can be executed:
It is a computer virus that does not live on the computer’s hard drive and instead dwells in an executable file. When the infected file is run, it spreads the infection to the other files on the system.
Polymorphic Viruses (also known as polymorphic viruses):
It is responsible for creating the thousands of copies on its own; in each duplicate, it modifies the sequence and byte values in order to avoid detection by antivirus programmes. Even the most sophisticated antivirus software may be unable to identify this malware. Polymorphic viruses have the ability to alter several data kinds and functionalities, and they are typically distributed by spam, infected websites, and the usage of other malware.
Rabbit Virus (also known as RAV):
It is sometimes referred to as a wabbit or a fork bomb. It has the capability of spawning new processes, and each of these new processes in turn spawns further new processes. This process continues until the virus has used all of the system’s available resources and the system is no longer able to provide further resources. It has the potential to cause the target system to slow down or crash. In the case of an infinite loop, for example, it spawns processes that use a large amount of CPU cycles and operating system resources on a regular basis.
Virus that hides in plain sight:
It is a computer virus that hides in plain sight and targets operating system functions specifically. This type of malware typically hides itself in partitions, files, or boot sectors, and it is capable of remaining undiscovered during antivirus or anti-malware scans, i.e., it may evade detection on its own will.
Symptoms of a Computer Virus include the following:
In the event that a computer is infected with a virus, there are several warning indications or symptoms that may be seen, some of which are as follows:
Slow computer performance: The machine may function slowly, for example, it may take longer to start up or shut down the computer, or it may take longer to open a file, document, or computer application, among other things. It is possible that the operating system and internet speed will become sluggish.
Pop-ups on a regular basis: A virus may create an unusually high number of pop-ups on your computer’s screen.
Problem with the hard drive: Even when the hard drive is not in use, it may experience unusually high activity. It has the potential to produce unintended modifications to your hard disc, as well as to freeze or crash this device.
The infected system may encounter numerous abrupt system crashes when one is playing games, watching movies, or performing other tasks on the infected machine. When the programme crashes, a blue screen shows.
The possibility of unwanted apps opening or starting automatically when you boot up your computer should be considered. These apps may be seen in the list of currently running applications on your computer. Occasionally, the window will close suddenly and without any apparent explanation.
Unusual activities: Your computer may behave in an unusual manner, for example, you may be unable to log into your accounts or remove corrupted files, and the Blue Screen of Death (BSOD) may display on a regular basis, among other things. Furthermore, the hardware, software, or operating system may begin to fail, resulting in the system being forced to crash unexpectedly.
A viral assault on your computer may cause your security solutions to malfunction. For example, antivirus software may fail to function properly when a virus attacks your computer.
A problem with the network: You may see heavy network activity even though you are not connected to the internet at times, or vice versa, depending on your configuration.
Unnecessary advertisement: We are used to seeing adverts when browsing the internet, but if you are seeing them even when you are not browsing, it may suggest that you have a virus on your system.
Trouble with your display: If your computer is infected with a virus, you may notice that the colours on your display have changed.
Applications Affected: Some viruses are specifically designed to infect and harm certain applications. As a result, some programmes may not function properly on your computer if it has been infected.
Internet access may be denied to a machine that has been infected with a virus if an antivirus site blocks access to it.
Dialog Boxes: A large number of dialogue boxes show on your screen at random intervals.
Problems with the printer: A printer connected to an infected computer may print documents without receiving a command or in an incorrect manner.
Homepage modification: It is possible that your home page will be modified without your involvement. For example, you could see a new toolbar on your screen, or you might be diverted to a different web address than the one you were on when you first came to the site in question.
Strange statements on a computer screen may include error messages, such as “cannot rename “folder” because a folder with that name already exists,” and other messages that are difficult to understand.