what are different types of computer infections?

A computer virus is a computer program written intentionally to enter a computer without any permission .The term “virus” is one type of program which can easily spread from one computer to another using external devices or any other way .

To avoid virus, you should never download from malicious websites. Always download from safe and legitimate ones. Never open emails or email attachments from strangers as they may contain malicious viruses that once executed can do massive harm to your computer.

To handle and remove virus you can take online virus removal support services and free virus removal software among other things.Considering that you need help understanding about a virus, its effects, and removal, we have brought a free virus removal guide for you.  

A virus should never be assumed harmless and left on a system. Most common types of viruses are mentioned below:

Different Types of Computer Viruses

There are various types of computer viruses which can be classified according to their  techniques, types of files they infect, where they hide, the kind of damage they cause, the type of operating system or platform they attack etc. Let us have a look at few of them.

Resident virus: This type of virus is a permanent in the RAM. From there it can overcome and interrupt all the operations executed by the system. It can damage files, programs which is opened, closed, copied etc.

Examples: Randex, CMJ, Meve, and MrKlunky.

Direct Action Viruses:

This type of virus is to replicate and take action when it is executed. When a fixed condition is met, the virus will go into action and infect files in the directory or folder that it is in as well as directories that are specified in the AUTOEXEC.BAT file path. This batch file is always located in the root directory of the hard disk and carries out certain operations when the computer is booted.

Examples: Vienna virus.

Overwrite Viruses:

This type of virus deletes the information contained in the files that it infects, rendering them partially or totally useless once they have been infected. The only way to clean a file infected by an overwrite virus is to delete the file completely, thus losing the original content.

Examples: Way, Trj.Reboot, Trivial.88.D.

Boot Sector Virus

This type of virus affects the boot sector of a floppy or hard disk. This is a crucial part of a disk, in which information of the disk itself is stored along with a program that makes it possible to boot (start) the computer from the disk. The best way of avoiding boot sector viruses is to ensure that floppy disks are write-protected and never starting your computer with an unknown floppy disk in the disk drive.

Examples: Polyboot.B, AntiEXE.

Macro Virus:

Macro viruses infect files that are created using certain applications or programs that contain macros. These mini-programs make it possible to automate series of operations so that they are performed as a single action, thereby saving the user from having to carry them out one by one.
Examples: Relax, Melissa.A, Bablas, O97M/Y2K.

Directory Virus:

Directory viruses change the path that indicate the location of a file. When you execute a program file with an extension .EXE or .COM that has been infected by a virus, you are unknowingly running the virus program, while the original file and program is previously moved by the virus. Once infected it becomes impossible to locate the original files.

Examples: Dir-2 virus.

Polymorphic Virus:

Polymorphic viruses encrypt or encode themselves in a different way (using different algorithms and encryption keys) every time they infect a system. This makes it impossible for anti-viruses to find them using string or signature searches (because they are different in each encryption). The virus then goes on creating a large number of copies.

Examples: Elkern, Marburg, Satan Bug and Tuareg.

File Infector Virus:

This type of virus infects programs or executable files (files with .EXE or .COM extension). When one of these programs is run, directly or indirectly, the virus is activated, producing the damaging effects it is programmed to carry out. The majority of existing viruses belong to this category, and can be classified depending on the actions that they carry out.

Examples: Cleevix and Cascade.

Companion Viruses:

 Companion viruses can be considered as a type of file infector viruses like resident or direct action types. They are known as companion viruses because once they get into the system they 'accompany' the other files that already exist. In other words, in order to carry out their infection routines, companion viruses can wait in memory until a program is run (resident virus) or act immediately by making copies of themselves (direct action virus).

Some examples include: Stator, Asimov.1539 and Terrax.1069

Multipartite Virus:

These viruses spread in multiple ways possible. It may vary in its action depending upon the operating system installed and the presence of certain files.

Examples: Invader, Flip and Tequila

Worms:
A worm is a program very similar to a virus; it has the ability to self-replicate and can lead to negative effects on your system. But they can be detected and eliminated by anti-viruses.

Examples of worms include: PSWBugbear.B, Lovgate.F, Trile.C, Sobig.D, Mapson.