Introduction to Malware: Part 2


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Viruses, Trojans, and Worms… Oh My!


When I started my tech support career with a major antivirus company, we were given a document with the above title. It wasn’t a large document, but it was one of the most important parts of the training. At that time, those three types of infections were really all there was to worry about, but even then most people really didn’t know the difference between them.
We all know the story of the Trojan War, where the Greek army pretended to retreat leaving a giant wooden horse as tribute to the city of Troy. Unknown to the Trojans, the horse contained soldiers who waited until Troy’s guard was down to slip out and attack.
So, it should be no surprise that when talking about an infection, a trojan gets onto your computer by pretending to be something you want. For example, you find a free download for an amazing application that will change the way you use your computer. After downloading it and running it, you get an installer error. What you don’t know is that what was really installed was a clever little program that will give someone access to your
computer or download other infections.
Unlike a virus, a worm does not infect files that already exist on your computer. Instead it simply makes a copy of itself, either on the computer or over a network spreading to other computers. The majority of worms spread using email attachments, sending itself out to potentially hundreds or thousands of computers from one host computer.
A common symptom of a worm is receiving emails marked “undeliverable”, caused when it tries to send itself to email addresses that don’t exist or are incorrectly formatted.
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