Computer viruses and its various types

 virus is a tiny software program that spreads from one computer to another computer and that interferes with computer operation. The term "virus" is also commonly used, to refer to many different types of malware programs. A computer virus is a computer program that can copy itself and infect a computer with no permission  of the user.

How they are spread:               
•     A computer virus may damage or delete data on a computer, use an e-mail program to spread the virus to other computers.
•    Computer viruses are most easily spread by attachments in e-mail messages or by instant messaging messages.
•    Computer viruses can be hidden as attachments of funny images, photos, games, greeting cards, or audio and video files.
•     Computer viruses also spread by using downloads on the Internet.
•    Computer viruses can be hidden in pirated software or in other files or programs that you may download.
•    A virus can only spread from one computer to another when its host is taken to the uninfected computer, for instance by a user sending it over a network or the Internet, or by carrying it on a removable medium such as a floppy disk, CD, or USB drive.

Different Types of Computer Viruses

  A virus should never be understood as risk-free  on a computer system. Most general  types of  viruses are given below -

E-mail viruses :-
An e-mail virus dealing as an attachment to e-mail messages, and usually replicates itself by routinely mailing itself to dozens of people in the victim's e-mail address book. Some e-mail viruses are launch when you view the infected message in the preview page of your e-mail software

The Worms :-
A worm is a small piece of software that uses computer networks and security holes to replicate itself. A copy of the worm scans the network for another machine that has a specific security hole.

The Resident Virus:- 
The resident virus is a stable as it dwells in  RAM. It can destroy programs and files that are renamed, copied, closed, opened etc.  From there it can overcome and break off all the operations executed by the system.
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The Direct Action Viruses:-
The main aim of direct action virus is to reproduce and act  when it is executed. When a particular situation is met, this virus will go to  infect files in the folder or directory.

The Overwrite Viruses:- 
This kind of virus is noticed when the fact that it deletes the information enfold in the files, folders and directory that it corrupt. The best way to clean a folder and files infected by this virus is to destroy the file completely.

The Boot Sector Virus:-
The boot sector virus have an effect on  the boot sector of a hard disk or floppy disk. It is very harmful for our hard disk. The only way of avoiding this viruses is to make sure that floppy disks and hard disk  are write-protected and not at all start your computer with an unknown disk  and floppy in the disk drive.

The Macro Virus:- 
This virus infect folder and files that are created using particular programs or application that hold macros.

The Directory Virus:- 
This viruses change the paths that point out the location of a file. the directory virus once infected it becomes impossible to locate the original files.

The Polymorphic Virus:-
Polymorphic viruses encrypt or instruct themselves in a different way using different algorithms and encryption keys every time they infect a system.
 

File Infector Virus;-
This type of virus infects programs or executable files. When one of these programs is run, openly or not directly, the virus is activated, producing the damaging effects it is programmed to carry out.

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 go with the other files that already exist.

FAT Virus:-
The FAT is basically a chart which contains numbers that correspond to cluster addresses on a hard drive. FAT virus attacks the FAT section and may damage crucial information.  A FAT virus can be rather dangerous as it infects a critical part of the computer's operational process.  

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. 

Web Scripting Virus:-
Many web pages include difficult code in order to create an interesting and interactive content.