Know your enemy- Computer Virus

The abbreviation of computer virus is - Vital Information and Resources Under Siege. Famous researcher Fred Chohen has named this. There are many kinds of computer virus like-

1. Trojan horse virus
2. Worm
3. Boot sector virus
4. Companion virus

5. Macro virus
6. Polymorphic virus
7. Stealth virus
8. Over writing virus
9. File infected virus
10. Mutating virus
11. Command purpose virus
12. General purpose virus
13. Multipurpose virus
14. Memory resident virus


Trojan horse virus: It is a dangerous virus. This kind of virus shows interesting/attractive messages. When a computer user clicks a trojan then it starts to spread like virus in humanbody. But without clicking it, a trojan can do no harm.

Worm: This type of virus gets in attaching with a file in computer. Then it makes it's duplicates and attacks special files. By this it hinders the work system of computer. The users who rely chat on internet are mainly attacked by worm.

There are two kinds of virus divided by working method.
1. Program virus     2. Boot sector virus

Program virus: This virus attaches their executable code in the first or last part of a file. For this, infected executable files' bite numbers are shown different from original numbers. Program virus replaces root programs' code with it's own code. When computer is started, this virus come in main memory and takes control of the system. In this condition, when other programs are opened, it attacks these programs.

Boot sector virus: Boot sector virus replaces hard disc's boot sector with it's own code and changes to a part of operating system. At first it stays in memory. Then it possesses boot sector. It obtains the boot sector's location by giving jump command in virus code. When computer is started, Bios program enters the boot area to get the boot record and controls the system.

Companion virus: Companion virus transforms .exe extension files to .com or .com files to .exe. This virus likes.com files most.This kind of virus changes a file's content without changing it's name.

Macro virus: It is a general type virus. It is written in macro language of application software like microsoft word. This virus attacks forming OLE/Macro. Macro virus often spreads through infected floopy, pen drive, CD/DVD, email attachment etc.

Polymorphic virus: This kind of virus fools virus scanners  by changing form. Cause there is no specific pattern in their codes.  These codes change via encrypting method.

Stealth virus: It is a partition kind virus. This type of virus can hide itself. For this, it is hard to identify and destroy it. It can disguise itself by using certain tactics to prevent being detected by anti virus. This virus replaces main file's important parts and possesses it's place without increasing the real bite numbers of the file. Hoel is a stealth virus which replaces 9216 bite from main program.

Over writing virus: This virus automatically overwrites itself in infected files. For this, at a time the infected file becomes impasse. This virus spreads very slowly. It is not so dangerous.

We can divide virus by attacking period.
1. Instant active virus: Computer becomes unworkable as soon as this type of virus attacks. Boot sector/partition table virus creates this instant problem.
2. Gradually active virus: This virus gradually accumulates in computer. Then it hinders the general works of computer.
3. Time bomb virus: This virus can hide for a long time in a computer. Then it becomes active in a specific time and causes harm. Example: Jerusalem- B virus.