Similar to motorists who travel at 10 miles per hour below the posted speed limit in the left-hand lane, programmers who deliberately create and distribute malicious computer programs don’t have a clue. They have a great deal of knowledge and expertise but they can’t seem to figure out how to function by simply following the rules. This article briefly explains how most computer viruses compromise vulnerable computers and how you can make your computer and valuable data much less vulnerable to a malicious executable or “virus.”
All malicious programs are “executable” files. On computers running MS-DOS or Windows based operating systems; .exe and .com are the common extensions for these files.
A Virus is a computer program created for the sole purpose of destroying data on your computer. The virus may destroy non-crucial files, or it may be programmed to erase all files. A virus can cause an infected computer to perform certain actions on certain dates or issue serious commands such as deleting your entire system registry, totally disabling the operation and booting up of your computer.
Viruses are distributed through executable files that we receive from friends, download off the Internet or even install ourselves. A virus will often come disguised as a Trojan which serves as the carrier for the virus.
A Trojan is a program that usually appears to be safe, but contains something harmful inside such as a worm or virus. You may download a game or an image, assuming that it’s harmless, but once you execute the file, the worm or virus goes to work. Sometimes they will simply annoy you, but many are specifically designed to cause severe damage to your system.
Worms operate a bit differently. These programs replicate themselves over and over again. Worms generally arrive through an email client. Machines become infected if the user accepts a Trojan file that contains a Worm in its payload. The majority of these programs are designed to exploit email address books stored on a mail server or hard drive. When you open a Trojan email attachment that contains a worm, the Trojan tells the worm file to propagate with all email addresses it finds and to email itself to each address, thus repeating the process.
The “Love Bug” is a good example of each of the above. It’s a Trojan because it arrives disguised as a “Love Letter” when it is actually carrying a harmful program. It’s a virus because once executed, it infects files on your computer, turning them into new Trojans. It’s a worm because it propagates itself by sending itself out to everyone listed in your email address book or IRC client.
Bacteria programs are simply designed to replicate themselves many times, thus causing a lack of resource or slowdown of the computer.
Spyware is usually designed to log marketing data from the computer and send it to a web-server which stores the information in a database. Because these programs are fairly easy to develop and distribute, they have become popular with identity thieves.
Similar to Spyware, Botnet applications are designed to copy software programs installed on individual computers and network computers within companies and organizations. Once a network has been exploited, the Master Botnet will usually command the Botnets that are located on the rest of the network and implement actions from the central server.