Whilst a biological virus may cause you sneezing, its computer counterpart may render sneaking in your personal details. If you discover some gradual or sudden loss of data on your hard drives, don’t wait for a hardware breakdown for counteraction, you may be under a virus attack; a computer virus attack. A Computer Virus is a malware or a malicious automated code which replicates itself from one computer to another and infects the operation of the machine. It is a small program which spreads by attaching itself (or forcefully by its designers) to executable files or documents present on the computer system.
Viruses are designed to be attached to files that have some programming capability. Such files are usually the executable files, for example files with extension .exe. Hence this advantage follows: A computer virus does not infect or target a machine unless the file it is attached to, gets executed by the user. So the good news is that it does not exploit the vulnerabilities in a system automatically. Besides computer virus, there are other types of malicious code like Trojans, worms, spyware, keyloggers and rootkits which are equally threatening but vary from virus in their dynamics. Read more about how computer virus works
The theory of self-replicating programs was first discovered by John Von Neumann; a Hungarian scientist in 1949. But it was only a proposed rhetoric and no evidence of violating virus was actually found till then. The first ever virus; Creeper Virus was detected on ARPANET (the then internet) in the early 1970s. It was written by Bob Thomas at BBN Technologies in 1971. However the violating PC viruses came into force with the spread of personal computers in 1980s. With the popularity of IBM PC (released in 1982) and APPLE Macintosh (released in 1984), real computers came into the market and hence came the epidemic of computer viruses like Brain, Vienna, Cascade etc. There was sudden drop-down of letters from the display, the computer would start playing some anonymous hymns, the boot sector of a floppy disc would be replaced by a copy of the virus or even the speed of the floppy disc drive would slow down.
Early viruses were pieces of small code attached to legitimate large files like popular games and word processor. Whenever the user runs these legitimate programs the virus loads itself into the memory. There it modifies other programs on the disc and add the virus’s code into the program.
Types of Computer Virus
Viruses are designed for various intents. It might corrupt or destroy data on your computer, use an email program to spread itself to other computers on your network or may even affect the boot sector. Broadly, computer viruses can be divided into two categories;
Compiled Viruses: It is that kind of a virus whose code is converted by the compiler into a format which can be directly executed by an operating system.
Interpreted Viruses: These are the more prevalent type of virus. Interpreted virus is composed of program or code which can be executed only by a particular application or service. These are comparatively easy to generate.
Below are some of the variants of the complied type computer virus:
1. Boot Sector Virus - As the name suggests a boot sector virus affects the boot section on your computer. Evidently, boot sector is the section which is accessed at the very first when the computer is turned on. It is used to boot the information used by the operating system. A Boot sector virus gains complete control over the Master Boot Record (MDR) or the DOS by replacing the contents of the OS with that of its own resulting in errors during booting or ‘cannot boot’ message. Michelangelo and Stones are some examples of boot sector viruses. Earlier, before the era of modern, heavy memory computers, floppy disks were used to boot the system. With the decline of floppy disks, boot viruses have declined as well.
2. File Infector Virus - This is the most popular and most prevalent variant of compiled computer virus. It attaches itself to executable programs such as word processors, game files, spreadsheets applications, etc. The file infector virus fixes itself into the host file and begins its operation whenever the file is executed. Here is a snapshot of one such threat detected by an antivirus.
When the file is executed, the virus runs first followed by the program. Examples of file infector virus are Cascade and Jerusalem.
3. Multipartite Virus - Unlike other types of viruses, the multipartite finds multiple breeding areas for target. It may attach itself to the boot sector, the executable files or both depending on machine variants like the type of OS and other variables. Some specimen of multipartite virus is Flip and Invader. Multipartite virus spreads faster than the other variants of compiled virus due to the presence of multiple spread vectors. Hence, removing these is also difficult and requires cleaning both the booth sector and the infected files.