Computer viruses are unwanted piece of codes or software programs that impede the functioning of a computer. They spread through infected files, insecure networks, and corrupt data. They can replicate and produce copies of themselves upon entering your system. These copies of a virus allow it to infect various files and spread from one application to another application of the system. It can travel from one computer to another computer through the transfer of corrupt and infected files via storage devices, communication networks, etc.
Given below are some of the types of viruses:
Overwrite virus
It is the simplest computer virus. It uses its own malicious code to overwrite the code of infected file. It does not change the size of the infected file even after replacing the content of the file completely or partially.
Macro virus
By this virus, the macros of a data file or document are infected or altered. It embeds itself as macro in a document and adds its own code to the macros. The virus gets spread when infected data files or documents are shared and opened in other computers.
Boot virus
Through this virus the boot sector program, stored in a storage device like hard disk, is altered. It uses its own malicious version of the boot sector program to replace the original boot sector program. The source of this virus is usually insecure computer networks, corrupt media files, and infected storage devices.
Resident virus
It resides permanently in the computer’s primary memory (RAM). When the computer is turned on, this virus gets active and corrupts the programs and files running on the computer.
Multipartite virus
It can spread and infect in multiple ways and has the capacity of infecting both the files and the boot sector.
File infector virus
It is one of the most common viruses found in a computer. It usually attacks executable files like: the files with .exe or .com extensions. When the infected file is executed the virus becomes active. The active virus then goes on to overwrite the file completely or partially. Therefore, it can destroy the file either completely or partially.
Computer worm
Though it is technically different from virus, it is similar to it in many ways. Like virus, it can replicate itself and spread but unlike a virus, a computer worm does not require a host program to spread itself. Because it can self replicate, it is capable of producing multiple copies of itself. The source of a computer worm is usually a network, for example if you send an email to an already infected email id; it can infect your email id as well.
Trojan horse
It is a malware just like a worm or a virus but on the technical aspect, it differs from both. It can easily replicate like a worm and virus. It hides or covers itself inside a program. The trojan horse would enter your computer once you install such a program. It has the capacity of providing unauthorized access of your computer to someone else, delete your files, send your files to some other computer, and make other unwanted changes to your computer.