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All you need to KNOW about PC viruses

By Ankur Jain
Last updated on: August 07, 2007 12:19 IST

Dangerous elements ahead! -- this sign is plastered all over the information highway, or at least it should be. The internet has no checks to oversee and control online goings-on, which makes it a veritable playground for troublemakers. And so, along with its uncountable benefits, the internet also brings a multitude of potential threats -- virus attacks, spyware, pornography, identity theft etc.

In this, the first part of our series on online threats, we take a look at viruses and how you can protect your computer and important data from virus attacks.

What is a virus?
Most computer users are aware of the damage a virus can inflict on their system, but aren't too clear on what exactly a virus is.

The main criterion for classifying a piece of executable code as a virus is that it spreads from one computer to another when its source of origination is taken to an uninfected computer without the knowledge or permission of the user. This happens mostly by users over a network or if a user has transferred it to a CD, floppy etc and uses the medium on a uninfected machine. Viruses commonly target executable files on the computer, which contain application software (MS Word etc) or parts of operating systems (Windows etc).

Not all viruses are designed to damage data, some are just created to make their presence known or to cause your PC to act up. Viruses can be divided into two types -- resident and non-resident viruses -- on the basis of their behaviour when executed.

Non-resident viruses immediately search for other mediums (computers, applications) that can be infected. They then infect these targets and finally transfer control to the application program that has been infected, thus allowing further transfer.

Resident viruses do not search for the other mediums when they run. Instead, a resident virus loads itself onto the computer's memory and transfers control to the host program. The virus stays active in the background and infects new hosts when relevant files are accessed by other programs or the operating system itself. The viruses are designed to be smart enough to employ various ways of hiding or camouflaging themselves.

Newer viruses can even avoid detection by fooling anti-virus software. A virus can hide itself by ensuring that a request of anti-virus software to read an infected file is passed to a virus, instead of to the operating system. The virus can then return an uninfected version of the file to the anti-virus software, so that it seems that the file is clean. Modern anti-virus software employ various techniques to counter this mechanism.

How can I protect my PC?
There's no way of being truly 100-per cent protected from viruses, especially when your computer is always connected to some form of network -- internet or local. But there are ways to avoid infection by following a set of simple guidelines:

~ Make sure that you have a clean bootable CD of the operating system at all the times.

~ If your operating system has an option of making a bootable CD, take the time to make one. You will appreciate the time spent if the need ever arises.

~ Use a reputed anti-virus solution and update it daily.

~ Make sure your anti-virus automatically scans any newly inserted discs for viruses, especially if you exchange data between your home computer and a publicly accessible PC.

~ Avoid opening e-mail with attachments unless you are absolutely sure they are from a trusted source.

~ If you are using an e-mail client on your computer such as Microsoft Outlook, Outlook Express or Mozilla Thunderbird, disable the message preview pane. This way you can filter the messages you open by the sender's name without letting the mail use any resources on your computer.

While the above steps cannot guarantee that your PC stays virus-free, they will ensure that your computer is better protected and better prepared for a virus attack.

Is my PC infected?
The problem with virus attacks is that unless your anti-virus rings the alarm bell, you do not have any way of being sure that your computer is not infected. Still, there are a few symptoms to look out for:

  • Your computer repeatedly stops responding when you try to use certain software. This could also take place due to corruption of an essential file required by that software.
  • You received an e-mail message that has a strange attachment. When you open the attachment, suddenly your system performance degrades.
  • Your anti-virus program is disabled for no reason and cannot be restarted. The computer may also block the re-installation of the anti-virus software.
  • Strange dialog boxes or message boxes appear on the screen.
  • Someone tells you that they have recently received e-mail messages from you containing infected files as attachments, while you are sure that you haven't sent any mail.
  • A program disappears from the computer, but you haven't uninstalled it.
  • The computer starts as expected some of the time, but at other times, stops responding before the desktop icons and taskbar appear.
  • The computer runs very slowly and it takes a long time to start.
  • Out of memory error message appears, even though your computer has plenty of RAM.
  • Windows restarts unexpectedly.
  • A partition on your PC completely disappears.

None of the above signs is a sure-shot sign of a virus infection, but if you do happen to notice one or more of these, get in touch with your software engineer immediately.

Which is the best anti-virus software?
Norton Antivirus, McAfee Virus Scan and Avast are the most popular anti-virus solution available today. Most computers come with an anti virus software installed, but you need to update it regularly by downloading the same from the website. If you think your PC might be infected or that the software isn't functioning as it should, get in touch with your software engineer immediately.


Ankur Jain