TYPES OF COMPUTER VIRUS:
They are classified into six groups:
1) Boot/Partition infecting virus:
i) Resident virus: Resident virus are those which install their code in the memory on execution & infect other programmes or disk from there.
ii) Non-resident virus: The first sector containing the code to load & start the operating system is called boot sector. These type of virus modify the boot sector.
iii) Partition table virus: The first physical sector in any sector in any harddisk is called master boot record, which contains booting information & also the partition table in formation in the hard disk. These virus modify the partition table & lead to unrecoverable data from the hard disk.
2) Executable fiile infecting virus:
-All virus modify, executable program files to replicate or spread are known as executable file virus. These virus infect the files with filename extension like .com, .exe, .dll etc.
3) Multipart virus:
- These virus infect both boot sectors as well as files. These are dangerous virus because they are infect all parts of the diskettes.
4) Directory infecting virus:
- These virus infect the directory information in any diskeette & spread quickly. These virus uses an undocumented DOS structure to point out the start of every executable
file to an area of the disk where the virus gets control & does whatever it is programmed to do and loads the original programs in a normal fashion. Here, it does not modify or damages files or boot sectors but infects the entire drives within seconds.
5) Hardware infecting virus:
- These virus can damage hardware. For example it can reprogramm the CRT chips to emit higher frequencies and can causes the monitor to burn out. Also some of the hardware infecting virus keep moving the hard disk drives heads randomly, this increased and unnecessary activity often damage the hard disk over a period of time.
6) Network infecting virus:
- These type of virus spread easily in a network environment. They may be a file virus, boot virus or a hardware virus. These virus are attached through the e-mail and downloaded programs.
