There are over 65,000 viruses in existence today with new ones being made and discovered every hour while anti-virus companies race against the clock to produce that every so vital counter measure. Exactly how much damage can a virus or spyware cause? In this two-part feature I will take a deeper look into the effects of viruses, Trojans and worms. I will also look at the different forms of spyware advertising and how a poorly configured firewall could ultimately be your PCs demise, or at a minimum unleash chaos on your computer.
I think it would be safe to say that the majority of the world's population knows what a computer virus is. On November 3, 1983 a man by the name of Fred Cohen conceived the first computer virus as an experiment to be presented at a weekly seminar on computer security. In the mid-eighties, two brothers who owned a computer store, wrote the first computer virus, a boot sector virus called Brain because they were frustrated with computer piracy. From these simple beginnings an entire industry of virus creation and distribution emerged, leaving us today with several tens of thousands of viruses.
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"Worms can spread very rapidly exploiting flaws in operating systems and networks and can not only infect a single PC but bring down entire networks." |
We have come a long way since the first virus was created and viruses have developed into a range of other malicious programs ranging from Trojans and worms to spyware and adware. A virus is a malicious computer code embedded within an executable program that victims activate on their machines, usually by opening an e-mail attachment or through a shared folder or file. Today the term virus is often used as just a reference to a malicious program or code that in actual fact may not even be a virus but some form of malware.
Below is a list f some of the worst viruses to have hit us and rendered us almost helpless in recent years.
Sobig.F
This worm first appeared in August 2003 and is by far the most widespread and fastest spreading malware in history. This worm propagates by mass-mailing copies of itself using its own Simple Mail Transfer Protocol (SMTP) engine.
Bugbear.B
Worm appeared in June 2003 and is a variant of the Bugbear.A. The worm spreads by sending emails containing attachments and by locating shared resources on your network to where it can copy itself too. The B variant may do a number of things such as logging keystrokes, opening a backdoor, shutting down anti virus and firewall programs and possibly steal information such as passwords and key-login data.
Klez.H
The Klez worm uses the Windows address book to send copies of itself to every address. The worm can also disable anti-virus software and infect executable files.
How Much Damage Can a Virus Cause?
To be classed as a genuine virus it must meet two criteria: it must be able to execute itself and must be self-replicating. Although not all viruses will do major damage some are created to delete files, reformat hard drives or to just make themselves known by presenting text, video or audio messages. Even if a virus does not cause major damage it may still affect your computer by taking up memory used by legitimate programs or causing system crashes.
There are five general forms of viruses that are categorized by the amount of damage they inflict:
File Infector Viruses
This virus attaches itself to an executable file. An executable file can be a program file, like Word or Excel, or a system file, like command.com. A file infector spreads when an infected executable file is run; other application files that are run subsequently then become infected.
Boot Sector Viruses
A boot sector virus is spread through infected floppy disks. This typically occurs when a user leaves a floppy disk in drive A. When the system is next started, the PC will attempt to boot from the floppy. If the disk is infected with a boot sector virus, that virus will infect the boot sector of the user's local drive.
Master Boot Record (MBR) Viruses
These viruses are memory resident viruses that infect disks in the same way as boot sector viruses. The main difference is that these viruses reside in the hard drive' Master Boot Record.
Multi-partite Viruses
These viruses have a dual personality, able to infect both boot records and program files and are rather difficult to repair. These viruses are quite malicious because of the number of ways it can spread and if you clean only the boot area and not the files, the boot area will be re-infected.
Macro Viruses
A macro is an instruction that carries out program commands automatically. Applications such as Word, Excel and Power Point make use of macros. It is this reason that macro viruses are the most common type of viruses. Macro viruses are macros that self-replicate. If a user opens a document containing a viral macro and executes this macro virus, it can then copy itself into that application's startup files. By doing so the computer is now infected and a copy of the macro virus now resides on the machine.
As I stated earlier in this article, a genuine virus must meet two criteria, execute and self replicate itself. It is this reason why the Trojan horse is not considered a virus as it can not replicate itself. For those historians out there you will no doubt remember that the Trojan horse was an instrument of war used by the Greeks to gain access to the city of Troy. So as you would expect Trojan horse files claim to be something desirable, but, in fact contain malicious code that when opened can cause loss or theft of data.
One of the most sinister types of Trojan horse is a program that claims to rid your computer of viruses but instead introduces viruses onto your computer. Trojans are also commonly used to open up ports, which will grant them access to your computer. Worms on the other hand are programs that can replicate themselves without using a host file and can jump from system to system. As we have witnessed in the past, worms can spread very rapidly exploiting flaws in operating systems and networks and can not only infect a single PC but bring down entire networks.
I hope that this glimpse into the world of viruses, Trojans and worms has provided some added knowledge and insight into one of the computers worst enemies. In part two of this feature, I will look at how intrusive and frustrating spyware can be and how it infiltrates your PC in a variety of ways. We will go inside a firewall and choose the perfect one for you. Until then watch out for those viruses - they are everywhere.
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