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What Is a Computer Virus?
Written by Houman Kargaran
Fri25 Sep
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The perennial hot topic for internet users is the computer virus. Computer viruses seem to be lurking everywhere  just waiting to steal your private details and crash your computer or favourite website.  It's scary, it's confusing, it might be on your computer and you may not even know it! But is it really that bad?

So what is a computer virus?
Virus is a software program that can grow and reproduce itself. Potentially a virus can cause permanent damage to your stored data, hard drive, or software packages.

Virus is transmitted between computers via the Internet or through removable storage such as CDs, DVDs, USB drives, and floppy disks, in most cases even without the knowledge of the recipient. Once you have a virus on your system it may be triggered just by opening a program, such as a spread sheet or a text file. Each time you open your program the virus is triggered and replicates itself.

Say you find a nifty little program on the internet that claims you can view your photos easily as well as fixing the red eye problem. It looks to be a useful program, but you soon notice weird things happening to your files. You might got a virus! Each time you open your new program the virus infects your system and damages your files. It is very simple and scary.

A short video of how viruses works

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Just like the flu, there are more "strains" of computer virus than you can poke a proverbial stick at.  Here are just a few:

Resident Virus
This type of computer virus will stay in your computer's Random Access Memory (Short term memory) permanently. It damages your files and every activity of your system such as opening, closing, copying, renaming a file, you name it.  If your computer has this type of virus you can kiss your operating system goodbye.

Direct Action Virus
The purpose of this type of virus is to breed and reproduce itself and listen to your activities.  When a specific environment is created (say for example a particular combination of key strokes such as "Command" "Z") it takes action. This virus infects your system files located in your long term memory (Hard Drive).  The infected files are those that support particular operations such as booting up your computer for example when your computer boots up you get the blue screen and nothing else. It looks like all your software has disappeared.

Directory Virus
This very sneaky virus changes the pathways of your files. Once your computer is infected with this virus it is almost impossible to locate your original files.

Polymorphic Virus
These clever viruses mimic real viruses by changing their nature every time they infect a different system. This makes it hard for anti-virus software to find and destroy them.

File Infectors
This type infects your programs only.  When you use the infected program you activate the virus and the damage starts. The majority of today's viruses are in this category.

Worms
Similar to viruses, a worm replicates itself and can do some damage to your system. Fortunately they are easily detected and deleted by anti-virus software.

Trojan Horses
This well known family of virus do not replicate without a specific trigger. Some will damage your computer but these days the Trojan Horse is used by companies to advertise on your computer while you are surfing the net. If you've ever been and bombarded by that annoying Advert that just won't seem to close, you've had a Trojan Horse virus.

Logic Bombs

As their name suggests, these can be very destructive. These lurk in a download or are copied from another computer. They stay in your system until certain environmental conditions are created, such as your anti-virus subscription expiring. When this bomb launches it deletes critical files which can devastate your hard drive.

The Melissa Virus Story

In 1999 the meddlesome Melissa Virus was created to look like a MS Word Document entitled "List.doc". The virus was uploaded onto a news group site. When people downloaded this document, the virus emailed itself to 50 friends and family members from the address book of the infected computer. When the recipients of this infected email presumably sent by their trusted source opened this email they too are infected and the virus again sends itself to 50 people from the host computer's address book. The sheer volume of emails generated forced major companies such as Microsoft to shutdown their email system, as their server couldn't cope with the traffic!

The good news amongst all the gloom is it is relatively simple to keep your computer virus-free.

  • Getting good anti-virus software is the obvious safeguard. It's important to regularly update your software once you have purchased it and to make an informed decision initially when you buy. It's easy to find reviews of these products online to make sure your anti-virus software is trusted and tested. Always use a registered commercial anti-virus protection and don't be tempted by unknown cheap or free Anti-virus software downloads.
  • Don't download programs from an unknown source or programs that have not been reviewed by other users online. These programs can easily carry a virus.
  • If you have Microsoft Windows, always make sure you enable the "Macro Virus Protection".
  • Never ever open an attachment that contains an executable file with the extension ".EXE" , ".COM", or " .VBS".
  • If you do open an attachment that contains such an executable program you could be infected and, if it's a nasty virus, lose all your data in minutes.
  • If you are really concerned about viruses you could change your operating system from MS Windows to a more secure one like Apple Mac, or UNIX, then you don't need to think about viruses.

Finally, to dispel a couple of virus myths: your computer cannot carry a virus by itself and anti-virus software companies do not create viruses to keep them in business!

 

Hooroo

Houman Kargaran

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