You should have heard about them. You probably would have read news reports on the damage they inflict around the world. Or, perhaps, you could have even had a first hand experience with them. If you have not, count yourself very lucky, for computer viruses, like their biological counterparts are capable of inflicting large amounts of damage.
A virus is a piece of computer code that that hides within other programs or documents so it can spread from computer to computer, infecting as it travels. Viruses can damage your software, your hardware, and your files. Viruses are often written with the intention of replicating themselves.
Viruses are triggered by the user’s action. For example when a person opens an email attachment a virus can be triggered off. Once triggered, viruses start bringing about damage to the computer instantaneously.
Here is a screenshot of an email message containing a virus-infected attachment:
Note that phrases like "no virus found" and "MCAfee OnlineAntiVirus” are used to convince the recipient and make him open the attachment.
Some of the newer viruses can be triggered without any user action. Certain types of viruses can be triggered by just reading an email or a visiting a web site. In this case, the viruses may be embedded in graphics, multimedia files or other downloaded components that happen simply by "receiving" or "loading" the files onto your email or browser software.
The type of damage caused by a virus depends very much on the motives of its creator. Therefore, some are just mildly annoying while others are downright destructive and are capable of bringing about severe damage. Viruses can perform various types of attacks on a computer and its files. A virus can, for example, delete files stored in your computer, write rude messages on the screen, make your computer emit weird noises or on a serious note, automatically send itself to your friends using your email program. Most viruses are programmed to attack the host computer as soon as they are executed. However, some viruses hide itself in your computer until a specific date to start the attack.
This flow chart summarizes the life cycle of a virus.
Creation
Virus program is created by a cybercrook.
Propagation
After creation, the virus enters a host computer. Then it replicates itself and copies itself to other computers.
Destruction
Then the virus attacks the host computer and delivers its ‘payload’.
Assimilation
The virus is discovered and the anti-software companies come up with protection against this virus.
Eradication
The protection methods are enforced by people to eradicate the virus.
File infector viruses
These are so-called the traditional form of viruses, as they have been around for a long time. File infector viruses, as the name suggests attack and alter the nature of executable (.exe) files or your system. This will prevent the user from being able to launch programs, which depend on these executable files. When the virus cripples critical files that are very important to your system, your computer’s operating system may crash.
File infector viruses are especially very dangerous because the virus can prevent the user from launching the browser and accessing the internet to remove the virus.
Boot sector viruses
These viruses attack the start-up area of your computer and overwrite a disk’s original boot sector data and replace it with an infected boot code of their own design. This makes it impossible to load your operating system and start your computer. Sometimes, these viruses allow the user to start his computer, but quickly spread to any of the other drives on the system such as a floppy disk drive or a network and infect them.
Macro viruses
Macro viruses use an application's own macro programming language to inflict damage. They target documents rather than programs.
Macro programming language is used to carry out highly specific tasks within a document. Unfortunately, they can also be used to infect and destroy documents. Opening a document that contains a macro virus will infect your system and the virus will spread to other documents on your computer. Macro viruses can be very destructive. This is because of the widespread use and share of data documents. Hence, macro viruses are capable of bringing about a wide scope of damage. Although people think many times about downloading unknown software from the internet, not many people hesitate to open a document sent by another user.
The first macro virus, written in Microsoft’s Word macro language, was discovered in August, 1995. Since a macro virus is written in the language of an application, any machine that runs the application the virus was written in, regardless of the operating system of the computer.
Retro Viruses
These viruses attack the antivirus software of a computer. These viruses will disable or corrupt your antivirus software so that the user becomes vulnerable to other common viruses and attacks.
Script Viruses
Script viruses are written in scripting languages that are used in websites, as well as in some computer applications. With the advent of the internet, these viruses are becoming more and more dangerous, as most of times, all that takes to activate them is accessing a webpage, containing the malicious code.
Others
Some viruses are created as relatively harmless pranks, causing the computer to display a message or to beep. Even these viruses are damaging because they degrade computer performance and waste your time detecting and removing them.
Not a month goes by without some virus scare. Millions of computers are affected by viruses every year. Viruses hit the corporate world especially hard. According to anti-virus firm, Trend Micro, virus attacks cost global businesses an estimated US$55 billion damages in 2003. That is a lot of money.
According to the Federal Bureau of Investigation, 99 percent of businesses have antivirus protection. Yet, in 2003, 82 percent were attacked by a virus. This shows the growing threat of viruses.
Unfortunately this problem does not look like it is going to go away soon. To date, more than 50 000 viruses have been catalogued and new viruses are being added to that list every single day.
There are many ways for a virus to enter your system. Some of the common ways are:
- Email attachments
- Some of your email messages may contain attachments that are infected with virus.
- Shared network files and network traffic
- These network files may again be virus-infected.
- World Wide Web (WWW) sites
- Some malicious websites contain viruses that are downloaded automatically into your computer, using flaws in your Internet browser.
- File downloads from the internet
- Shared Floppy disks, CD-ROMS and ZIP Drives
- A virus can enter your system when you transfer virus-infected files from one computer to another.
- Pirated software
- Certain pirated software may cripple your computer due to certain malicious programs that comes bundled with the software.
Sometimes, you may not even know that your computer is being affected by viruses. This often happens when you do not have proper anti-virus software installed, or you do not scan your system regularly for viruses. Anyway, here are a few signs that you should look out for:
- Programs exit or ‘hang’ suddenly
- Frequent error messages appear on screen
- Others informing you that you have been sending out strange emails, while in fact, you did not.
- Certain files in your computer become inaccessible or disappear
- Your computer emits weird sounds
- Strange messages and pictures pop up on the screen
Reference
How Does a Virus Work? by Matthew Ferrara
http://www.mfseminars.com/av/av-how.htm
Types of viruses
http://www.jconsult.com/virus/smex38help/WebRoot/at.htm
Error messages
http://www.smartcomputing.com/techsupport/detail.aspx?guid=&ErrorID=23246
About Viruses
http://www.pandasoftware.com/library/IntroVir.htm
Viruses
http://www.tufts.edu/tccs/support/virus.shtml