As already mentioned in previous posts of this site, viruses are the major factors which help in the destruction and hacking of data and information which are stored in a computer’s memory. In this post, we have tried to make our visitors and readers well known about the types of viruses on the basis of their residential areas. So, we have enlisted and described the different types of viruses in the lines below:
- Boot sector infectors: These are the viruses which reside in the boot sector of the hard disk or partition table of hard disk of a computer. Some examples of such viruses are C-Brain, Stone/Marijuana, 8290 (Print screen), Joshi etc. The instructions for booting are stored in the boot sector (side 0, sector 1, track 0 of the bootable disk). The ROM BIOS program searches for bootstrap program in this location. The virus program puts the original boot sector containing the bootstrap program somewhere else on the disk. So, unwittingly, the ROM BIOS loads the infected boot sector into the RAM and passes control to the viral program. The virus first of all executes its own program, becomes memory-resident and takes control over the important system parameters of the computer. Then it loads the original boot sector and transfers the control to DOS. It keeps a watch on use of disks and infects any uninfected disks as soon as it is used.
- File infector viruses: File infector viruses are such kind of viruses which attach at the start or the end of executable COM or EXE files of computers. When the infected file is executed, the virus code gets executed first, takes control over the system parameters and resides in the RAM. After that, it remains in the RAM and keeps a constant vigil for executable files. Whenever such type of file is run, the virus infects it. These viruses are the most dangerous ones, as far as replication is concerned. In a heavy user environment, a large number of files are infected within a short period of time.
File infector viruses can be further categorized into Direct Action File Infectors and Indirect Action File Infectors.
- DOS system infectors: These viruses affect the DOS (Disk Operating System) and its files like IO.SYS, MSDOS.SYS and COMMAND.COM. They enter the system in the guise of device drivers which are loaded into memory before any other program and remain in the memory till the time when the computer is shut down. Most of these viruses are written in Assembly language. A virus program should be as small as possible so that it can hide in a small place in the disk. The most efficient viruses should contain good replication capacity and a great destructive capability within minimum number of instruction.
- Message carrying viruses: Message carrying viruses are not specialized for the destruction and infection of data and information of a computer. They are just involved in annoying and disturbing the computer users during operations.