Before spring break one of our teachers was convinced that her computer had a virus. Every few minutes a message would pop up saying that her computer had one. Most people call any type of malicious software a “computer virus,” which is OK and certinaly descriptive, but not quite accurate. Viruses, worms, and trojans are different types of malicious software with different behaviors. In particular, they spread themselves in very different ways. Malicious software in general is referred to as “malware.” If you want a catch-all term for bad computer software, malware is the word to use.
Viruses Infect Other Files: A computer virus infects other files, similar to how a biological virus infects living cells. When you execute a virus by running an already-infected file, the virus infects other files on your system. In most cases, it adds itself to existing .exe files on your system, so it will run when they do. Viruses also wreak havoc on your system. In some cases, they may replace existing program files with themselves entirely, instead of just adding themselves to the existing programs. They may delete files, and take up system memory and cause crashes.
Worms Copy Themselves: A worm is a standalone program that doesn’t require user intervention to spread. Worms don’t infect existing files – they spread copies of themselves instead. Some worms, like the infamous Mydoom worm, email copies of themselves to every address in a computer’s address book. Some of the most dangerous and fast spreading worms, such as the Blaster and Sasser worms, exploit vulnerabilities in network services. Instead of emailing files, they travel over the network and infect unpatched systems that aren’t running firewalls.
Trojans Lie In Wait: Trojans are named after the mythological trojan horse. A trojan horse is the same sort of thing. Trojan horses masquerade as useful software, such as a legitimate program. Instead of being well-behaved software, a trojan opens a backdoor on your system. The trojan’s author can use the backdoor to make your system part of a botnet, use your Internet connection to perform illicit activities that will be traced back to you, download other malware programs onto your system, or do anything else they want.
Spyware spies on you: Spyware encompasses everything from “key loggers” that log your keystrokes to steal your credit card information and online banking passwords, to advertising programs that monitor your web browsing activity and send it over the Internet. Spyware is generally designed to make money for its creators.
Scareware, also known as Crimeware: Scareware often appears as a fake antivirus alert on a web page. If you believe the alert and download the fake antivirus program, which is what our teacher really had on her computer, it will inform you that you have viruses on your system, of course. The antivirus program asks for a credit card number, insisting on a payment before “fixing” your system. Scareware holds your system hostage until you pay or remove it. All was well after a little cleaning on her computer.
Our district does a very good job of protecting the schools computers, but some can, and do, slip through.