What is a Computer Virus?

Computer Virus


What is a computer virus?
A computer virus is a small software program developed the bad guys. It spreads from one computer to another leaving infection as it travels, interferes with computer operations, corrupts or deletes data on a computer and may use an e-mail program to email itself to other computers, or even delete everything on the hard disk...

Computer viruses are most easily spread by attachments in e-mail messages, by IM messages, can be disguised as attachments of funny images, greeting cards, or audio and video files, by downloads on the Internet or hidden in pirated software. So don’t open an e-mail attachment unless you know the sender don’t download unnecessary software or a software which you never heard of.

Symptoms of a virus infection:
The following are some primary symptoms of infection: 

• The computer is slower than a turtle.
• The computer freezes, locks up frequently, crashes,
• If the computer restarts every few minutes.
• The computer restarts by itself. 
• The computer does not run as usual.
• Applications on the computer do not work correctly.
• Disks or disk drives are inaccessible.
• You cannot print items correctly.
• You see unusual error messages.
• You see distorted menus and dialog boxes.
• There is a double extension on an attachment that you recently opened.
• An antivirus program is disabled for no reason, cannot be restarted, cannot be installed on the computer, or the antivirus program will not run.
• New icons appear on the desktop by itself, or the icons are not associated with any recently installed programs.
• Strange sounds or music plays from the speakers unexpectedly.
• A program disappears from the computer even though you did not intentionally remove the program.

To be simple you will have a creepy feeling that your computer is haunted. However, these signs may also be caused by hardware or software problems that have nothing to do with a computer virus.

Types of virus:

Resident Viruses

These viruses will reside on the RAM memory situated in the CPU, and will damage or corrupt all those files and programs available on that system.

Direct Action Viruses

These kinds of viruses will affect the documents in the folder or directory and replicate them again in the same place where it is located in. The execution of the virus is triggered when the system is booted every time.

Overwrite Viruses

These viruses damage or remove the data present on those documents that it infected and thus making it useless at last. The only option to do from here is to delete that useless file.

Boot Virus

The virus that infects part of a hard disk or a floppy drive referred to as boot sector, the crucial part of the disk where the operating system and boot programs will be stores. The boot sector viruses are executed when the computer is restarted. These viruses are almost extinct as people stopped using portable floppy discs.

Directory Virus

These viruses are designed to change the location of the infected file and so when you execute it, you will never know that you have run a virus.

File Infectors

These are the common PC viruses that are designed to affect executable files and application programs. Usually, these viruses accompany the free stuff you download online.

Companion Viruses

The name suggests the characteristics, as these viruses will always be accompanying other files that were already present on the PC.

FAT Virus

File Allocation Table is the full form of FAT. FAT viruses when executed will result in loss of data.

Worms

These are similar to computer viruses but are less effective and easy to remove. These replicate themselves and reduce the system performances.

Trojans or Trojan Horses/Logic Bombs

The viruses that do not replicate and are designed to perform targeted activities.

What is a Trojan horse?
Trojan Horses are a type of computer program that appear to perform a certain function, but actually perform other when you run it, often malicious actions (it may erase your hard disk). Trojan horses doesn’t replicate automatically. It may reformat the hard disk, delete files and programs, install hidden programs, such as pirated software, reduce security and enable intruders to remotely access the computer or the network.


What is a Worm?
A worm is similar to a virus by design and is considered to be a sub-class of a virus. Worms spread from computer to computer, but unlike a virus, it has the capability to travel without any human action. The biggest danger with a worm is its capability to replicate itself on your system, so rather than your computer sending out a single worm, it could send out hundreds or thousands of copies of itself creating a huge army of worms with devastating effect. One example would be for a worm to send a copy of itself to everyone listed in your e-mail address book. Then, the worm replicates and sends itself out to everyone listed in each of the receiver's address book, and the manifest continues on down the line.

What is Spyware?
Spyware can install on your computer and collect small pieces of information about users without your knowledge. They are hidden from users and may be difficult to be found. These programs can change your computer’s configuration or collect advertising data and personal information. Spyware can track internet searching habits and possibly redirect web site activity. 

Symptoms of Spyware:
Spyware may result in:

• Slow internet connection.
• Changing your web browser’s home page.
• Loss of internet connectivity.
• Failure to open some programs, including security software.
• Unable to visit specific websites, which may include redirecting you to another one.

How to avoid being infected by virus?

• Install a reliable anti-virus program
• Activate firewall on your computer/network
• Frequently update anti-virus program
• Update your OS regularly
• Don't open mail attachments without scanning
• Don't boot from an unknown data CD
• Scan files for viruses before using them
• Don't download unreliable software
• Don't download software from unreliable websites

To know more, read "How antivirus works?" and "What is Virus signature?"