Types of Computer Viruses

You are already aware of what computers are and what functions they perform. Being a part of this modern era, you must come across with the term “Computer Virus” many times, which is the basic cause of computer infection. It corrupts the computer files and affects its functioning. A virus can spread from one computer to another by means of network or by any removable medium like CDs, DVDs, Floppy and USB Drives, which may carry virus. The spreading of the malicious code of these viruses is generally facilitated by the internet.
A virus is a computer program that can easily replicate itself and cause computer infection. This software is written deliberately to make its entry in a computer without any notification or permission of the user. These nasty programs install themselves. There are various types of viruses, which depends on the malicious effect they cause. Not all are equally malicious but the user should check that it is removed as soon as possible, no matter it is more or less harmful. The most common types of viruses listed and explained below. Just have a look.

Resident Viruses

It is one of the most common types of virus, which resides in the computer memory also known as RAM. The function, which it performs, is to infect the already installed programs and the programs, which may installed in future. This all happens by incorporating a malicious code in the memory of the computer. They achieve this by allocating a space for them in the memory of the computer. The viruses can affect the other files only by establishing a process, which can activate the malicious code to function. There are various types of processes, which developed by the viruses to start its functioning. The most common of them is TSR (Terminate-Stay-Resident) interrupt function and manipulation of MCBs (Memory Control Blocks). The TSR interrupt functioning method is simplest for the virus to arouse infection but the scanners can also detect it very easily. This interrupts all the executions by corrupting programs and files that closed, opened or renamed.

The detection is very easy as it achieved by referring to the local hard drive’s map. The resident virus detected by antivirus with in-depth scanning efficiency only. The examples of this type of viruses are Meve, Mrklunky, Randex and CMJ.

Overwrite Viruses

This type of viruses infects the wide range of operating systems such as Macintosh, Linux, Dos and windows. The virus generally attacks a file, which becomes its victim and after this, the virus overwrite the file with the malicious code. If the infection not detected on time, the infected file can cause damage to the other files irreversibly. The computer system infected with such type of virus becomes inoperable and do not perform functions normally. The infected files cannot disinfect but the only thing can happen is the removal of the corrupted file and restoring it from the backup resource. The examples of this type of viruses are Trivial.88.D, Way, Trj.Reboot.

Direct Action Viruses

When this virus is executed in the computer it starts replicating and taking action on the files and directories. These infect the files in a directory and also the directories having those files that are specified in the AUTOEXEC.BAT file path. Generally, batch files of this type are located in the root directory of the hard drive and it also performs some functions when the computer is booted.

Boot viruses

These are the viruses which affect the boot sector of the diskettes and the hard drives. Every hard drive or diskette has sectors and the first sector is known as the boot sector. It has MBR (Mater Boot Record) which functions to read and load the OS (Operating System). If you re-boot the computer while the disk having virus infected boot is in the drive then it can cause infection to the hard drive of the system. As soon as the hard drive gets infected, all the diskettes will automatically get infected. You can check this virus by using antivirus software.

Polymorphic Viruses

This is one of those types of viruses which are very complex threats to computers. Every tome they infect the computer system, they produce copies of themselves by encrypting or encoding them is a different way. All the copies are functionally active but slightly modified of the previous one. To encrypt in a different way, they use different encryption keys and algorithms. This is almost impossible for the anti-virus to check them while doing string or signature searches because they are totally different in each encryption. They can also create huge number of copies of themselves.

The examples are Elkern, Satan Bug, Marberg, tuareg.

File Infectors

These are the types of viruses which include many other viruses and these basically infect the programs and executable files such as files with .EXE or .COM extension. The virus gets activated as soon as the file is run directly or indirectly. After the activation it starts affecting the other files for which purpose it is programmed.  These viruses are further classified depending on the type of infections that they cause.

Trojan Horses

The name of this virus comes from the Greek mythology according to which Trojan horses are the wooden horses used by the Greek soldiers so as to get into the city of Troy. This is a program which is downloaded by the user either with any useful downloading or by mistake. After opening into the computer the virus makes a backdoor into the computer. With its help hackers can easily access your computer and can incorporate as many viruses or software as they want.

Companion Viruses

This is another type of viruses which can cause great danger to your computer system. Unlike others it does not modify the existing files rather it creates new files and spread the malicious code with their help. This is unknowingly executed in the system and when the time comes to spread the infection it searches for the file labeled MGM.EXE.  After this it creates the files with the same label.

The examples are Terrax.1069, Stator etc.