A virus is a program designed by a computer programmer (malicious hacker) to do a certain unwanted function. The virus program can be simply annoying like displaying a happy face on the user's screen at a certain time and date. It can also be very destructive and damage your computer's programs and files causing the computer to stop working.
The reason why hackers create viruses are open for speculation. The most quoted reason is simply to see if it can be done. Other reasons are Ludite based "smash the machine" motivations, antiestablishment/anti-corporate actions, criminal intent, and various others that range into the "conspiracy theory" realm.
Viruses take two basic forms
One is a boot sector viruses which infect the section of a disk that is first read by the computer. This type of virus infects the boot or master section of any disks that it comes in contact with. The second is a program virus that infects other programs when the infected program is run or executed. Some viruses infect both and others change themselves (polymorphic) depending on the programs they encounter.
Though viruses do not damage computer hardware there have been attempts to create programs that will do things like run the hard drive until it fails or lodge itself in the computer's clock (which has a rechargeable battery) allowing it to remain active even months after the computer has been unplugged. Other viruses affect certain microchips (BIOS chip for instance). These microchips need to be modified under normal computer use but the virus program can produce changes causes them to fail. Other viruses will affect the characters or images displayed on the screen which may give the impression of monitor failure.
Viruses can cause a great deal of damage to the computers it infects and can cost a lot of time and money to correct it.
Computer viruses have been around for a long time, even before computers became widely used and they will likely remain with us forever. For that reason computer users will always need ways to protect themselves from virus programs. The main, common feature of a virus is that it is contagious! Their sole purpose is to spread and infect other computers.
A computer gets a virus from an infected file.
The virus might attach themselves to a game, a program (both shareware and commercial) or a file downloaded from a bulletin board or the Internet.
You cannot get a virus from a plain email message or from a simple text file! That is because the virus needs to be 'run' or executed before it can take effect. This usually happens when the user tries to open an infected program, accesses an infected disk or opens a file with an infected macro or script attached to it. A plain email message is made up of text which does not execute or run when opened.
Modern email programs provide the ability to allow users to format email messages with HTML and attach scripts to them for various purposes and it is possible for a malicious hacker to attempt to spread a virus by building a virus script into an HTML type of email message.
When you are accepting software or scripts on Internet sites or reading mail from unknown senders it is best not to run a program from that site or sender without checking it with an anti-virus program first.
You can take safeguards against virus infection. The first thing is to get an anti-virus program. Most reputable companies that create virus protection programs release an evaluation copy that a Internet user can download for free and use for a certain amount of time. This anti-virus program will be able to check your computer for the viruses and repair damage or delete files that are infected with viruses. You may have to replace infected files that cannot be repaired.
The second thing you can do is purchase a copy of the program. The reason for this is that viruses are constantly being created. When you purchase an anti-virus program you are also purchasing periodical updates which keep your anti-virus program up-to-date and able to deal with new viruses as they are encountered. Commercial virus programs also allow the user to customize when and how the program will check the computer for viruses. You will need to renew this updating service periodically.
If you find that your computer has been infected with a virus use an anti-virus program to clean your computer and make sure to check all the disks that you use. This includes all the hard drives on your computer(s) and all your floppy disks and CDs as well as any media that you save information on. Remember that the virus can easily re-infect your computer from one infected file!
If you have to reload your computer programs, use the original program disks. You may want to check your original disks before reinstalling the software. If your original disks are infected contact the distributor to get replacements.
Always take the time to ensure that your computer is properly protected. Spending money on a good virus checking program could save you hundreds of dollars and lots of time later.
A discussion of viruses would not be complete without mentioning hoaxes. Malicious people without programming skills will send out fake virus warnings causing people to take unnessary measures which often cause your computer harm. One example tries to get the unsuspecting computer user to delete an important system file by warning them that it is a virus. A legitimate virus warning will provide a link to a website operated by an anti-virus company with more information about that virus. Don't forward a virus warning until you have check out whether it is legitimate.