A Computer Virus is basically an executable program, which may cause serious damage to a computer software, as well as hardware. Depending on the nature of the VIRUS, the intensity of the damage may increase. Most of the viruses can cause severe damage to the computer hard disk.
According to the definition of computer virus, it is an executable program that can reproduce itself. This means, it is like an infection or cancer in human bodies or human cells. Once a virus has entered into a computer, it immediately starts spreading by multiplying itself. The replication is intentional; the program is structured in such a manner that it can copy itself. Computer viruses can transmit from one system to another through different mediums like internet, USB devices, etc. Mostly, it is a threat for the internet users, as this can transmit through FTP or File Transfer Protocol, and sometimes even through the email attachments as well.
Computer Virus History
In the year 1982, the first computer virus was programmed. This program was constructed and written by Rich Skrenta. This virus was generally known as Elk Cloner. It was programmed in such a manner that it could attach itself to Apple DOS OS, thereby, spreading by the means of floppy disks. Soon, a few more of such virus programs were introduced. One of the popular primitive computer virus programs is Brain. This is basically a boot sector virus, created by two brothers, Amjad Farooq Alvi and Basit. It was the year 1986, when ‘Brain’ appeared for the first time.
Computer Virus Classes
A virus must be permitted to write to the computer memory or execute the code, so that, it can replicate itself. This is the reason why many viruses come associated with an executable file. This file must be a part of the legitimate program. Computer Viruses can be broadly classified into two classes. They are, the resident Virus, and the non-resident virus.
Resident Computer Virus
This is a common type of computer virus. These viruses are basically stored into the infected computer hard drive via a file. As these viruses are stored directly into the computer, they can start functioning the moment the computer is on or the file host is run.
Non-Resident Computer Virus
Unlike the resident viruses, non-resident viruses are not stored into the hard drive of the computer. These viruses are sheltered by some executable files. Whenever, that file is run or accessed, the virus program starts being executed.