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Loyola University Chicago

University Information Security Office

Computer Viruses

What is a computer virus?                                                                                                             
A computer virus is a program designed to do bad things to your computer. They attempt to trick you into opening an infected file or visiting an infected website, or take advantage of unpatched holes in your computer's operating system. The methods that it uses, and the bad things that it performs, vary from virus to virus and variant to variant - we'll touch on those later. Some of the examples of what a computer virus will do range from destroying your files to using your computer to send spam to recording all of your keystrokes to later allow someone to try and access your bank accounts or steal your identity. Viruses will also attempt to use your computer to send out more copies of itself.    If you think you have a virus on your computer, call the Help Desk at 8-4ITS.


What is a worm?                                                                                                                                 
A worm is like a virus, in that it is designed to do bad things to your computer and that it will use your computer to attempt to send out more copies of itself. The difference lies in how it spreads. A virus requires some human intervention to spread, such as opening an infected attachment. Instead of relying on human intervention, a worm will exploit a vulnerability in your computer to automatically infect your machine. As you.ve probably guessed, this allows worms to spread much faster than viruses. For example, Melissa was one of the "more successful" viruses, and took 3 days to spread to 100,000 computers. An example "successful" worm is Code Red, took just over 15 hours to spread to the first 100,000 computers and infected over 340,000 computers in the first 24 hours.


What is a trojan horse?                                                                                                                      
A trojan horse is a category of viruses. This type of virus will pretend to be something other than what it really is. For instance, viruses will often pretend to be a collection of pictures of a celebrity. This leads a curious user to open the file, hoping to see the pictures. Instead, the user has just launched the virus on their system. More sophisticated trojan horses will actually contain the files, or in this example pictures, while infecting the computer in the background without the user's knowledge.


How can I protect myself?                                                                                                                 
There are three major elements to protecting yourself - use antivirus software, automatically patch your system, and be careful about what you click on. Following the instructions and advice in those links will protect you from many viruses, worms, and trojan horses.


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