Computer Terms
 Computer Virus

  Computer Virus
Learn few informations about Computer Virus

Computer Virus | Types of Computer Virus | Some Common Computer Virus's Nature

Computer Virus

Virus is a group of willfully destructive or self-duplicating computer program which interferes with a computer's hardware or operating system. They are designed to duplicate or replicate themselves and to avoid detection. When a virus is executed then computer follows the instructions given by the virus. It tries to replicate by various means like floppy disk and hard disks and tries to infect it's files. It can also attach itself to e-mail messages and spread across computer networks by infecting other shared drives. Some viruses can also reside on the portions of the hard disk or floppy disk that loads and runs the Operating System automatically.
Viruses are created to prevent software from being pirated, steal and scramble valuable data's, and to entertain users by producing interesting messages, greetings, or nude pictures on the screen. Generally, there are five categories of viruses. They are parasitic viruses, bootstrap sector, multi-partite, macro, and script viruses. Millions of computers are infected with viruses and billions of money are lost to clean it or bring under control. Several types of antivirus software can be used to detect the presence of infected file by virus. To prevent from viruses, others floppy disks or CD's should be scanned properly. In order to recover from virus infection, it must first be eliminated. Some examples of antivirus software are Norton Antivirus, MacAfee, PC-CILLIN, Virus Buster, etc.
These computer viruses was started in AT & T's Bell Laboratories, engineers used computer virus as entertainment after the work. In 1988, this program was found in Pentagon, the American Secret Agency Department and NASA.. These software are dangerous to data as it corrupts data and information. They basically change the file size, slacken the processing capabilities of the computer itself, steal data which can be used by the programmers for their use, scramble data and file from one computer to another.

Types of Computer Virus

Generally speaking, there are five categories of viruses. They are shown below by numbering:

  • Parasitic or File Viruses
  • Bootstrap-Sector Viruses
  • Multi-Partite Viruses
  • Macro Virus
  • Script Viruses

Some Common Computer Virus's Nature

Parasitic or File Viruses : Parasitic of File Viruses infect executable files or programs in the computer. These files often identified by the extension .EXE in the name of the computer file. File viruses leave the contents of the host program unchanged but attach to the host in such a way that the virus code is run first. These viruses can be either direct-action or resident. A direct-action virus selects one or more programs to infect each time. A resident virus hides in the computer's memory and infects a particular program when that program is executed.

Bootstrap-Sector Viruses : Bootstrap-Sector Viruses reside on the first portion of the hard disk or floppy disk, known as boot sector. These viruses replace either the programs that store information about the disk's contents or the programs that start the computer. Typically, these viruses spread by means of the physical exchange of floppy disks.

Multi-partite Viruses : Multi-partite Viruses have combine abilities of the parasitic and the bootstrap-sector viruses. They are able to infect either files or boot sectors. These types of viruses can spread if a computer user boots from an infected diskette or accesses infected file (s).
Macro Viruses : Macro Viruses infect programs that contain powerful macro languages, programming languages that let the user create new features and utilities. These viruses are written in macro languages and automatically execute when the legitimate program is opened.

Script Viruses : Script Viruses are written in script programming languages, such as _VB Script (Visual Basic Script) and _JavaScript. These script languages can be seen as a special kind of macro language and are even more powerful because most are closely related to the operating system environment. The famous example of script virus is "I LOVE YOU" virus, which appeared in 2000.

Time Bomb Viruses : Time Bomb Virus stops working of a program. The virus contains information for damaging the particular sections of .COM or .EXE files at fixed dates as described in views program. As the date arrives, the program gets corrupted or may not be corrected and the program will simply stop working. You have to purchase or buy a new package once again.

Logic Bomb Viruses : Logic Bomb Virus is another type of virus which destroys the data, in case logical operations are to be performed in data processing or program generation. It has such an instruction that on the fixed date, in a fixed section of disk, a fixed number of data are destroyed. For e.g.: On the 28th September 2005, Wednesday - 1,024 Kilo Bytes of data destroyed by this virus.

Trojan Horse Viruses : Trojan Horse Virus acts like the Trojan horse of Greek mythology. This virus program is hidden inside another apparently useful program. While the useful program is executed, the hidden part does something nasty, like erasing FAT and directory. It does not affect if the software is purchased from a reliable source which has a license. If the software is pirated, the hidden virus program is activated and the important part of the program is corrupted automatically. As you go on copying the pirated software, the virus infection goes on increasing until one day, the program will stop working.

Worm Viruses : Worm Virus resides on one side of the sector or track of the disk just like worms residing in the hosts. The virus corrupts the data and instructions required for the execution of the software.