Introduction to Viruses

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Introduction to Viruses

      Computer viruses may seem mysterious, even frightening, but are actually quite easy to understand. I’ll try to shed some light on: how viruses work, what they  really are, and some steps you can take to keep you and your information safe.                                                                                                                                       Viruses are simple, once you understand what they can and can’t do; it’ll be that much easier to protect against them.

      Do you have anti-virus software on your computer? You should. If you don’t get some, if you do, why should you need to understand any of this? The best reason is an informed consumer has the knowledge to judge if the anti-virus software they’re using is giving the protection you think it is. Another reason is that viruses are only one threat to your programs and data; we’ll explore how to protect ones self fully. Are viruses a serious threat, our just hype? Viruses and anti-virus programs are not the complex, hard to understand software they’re made out to be. Not only can the programs be understood by anyone, but these days, it’s critical that we all grasp how they work so we can protect ourselves. If you have a virus, you are no longer in control of your PC. Almost all viruses can cause damage to your files- mostly because the viruses themselves are poorly written programs. If a virus destroys nothing else, it does destroy your trust in your PC- you feel violated.

Virus Types and What They Infect

      Viruses come in many types; written using many different infection strategies. A virus is a program which reproduces its own code by attaching its self to other programs in such a way that the virus code is executed when the infected program is executed. Viruses do this without the permission or knowledge of the user. Viruses have multiple characteristics and fall into multiple categories.


  • System Sector Viruses

             These infect control information on the disk itself.

  • File Viruses

             These infect program (COM and EXE) files.

  • Macro Viruses

             These infect files you might think of as data files. But,

             because they contain macro programs they can be infected.

  • Companion Viruses

            A special type that adds files that run first to your disk.

  • Cluster Viruses

            A special type that infects through the disk directory.

  • Batch File Viruses

            These use text batch files to infect.

  • Source Code Viruses

            These add code to actual program source code.

  • Visual Basic Worms

             These worms use the Visual Basic language to control the

             Computer and perform tasks.

How Viruses Infect

      Viruses are also categorized by how they infect. These categorizations often overlap the previous categories mentioned, and may be included in the description (e.g., polymorphic file virus).These categories include:

  • Polymorphic Viruses

            Viruses that change their characteristics as they infect.

  • Stealth Viruses

Viruses that try to actively hide themselves from anti-virus or

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system software.

  • Fast and Slow Infectors

Viruses that infect in a particular way to try to avoid specific

Anti-virus software.

  • Sparse Infectors

Viruses that don’t infect very often.

  • Armored Viruses

Viruses that are programmed to make disassembly difficult.

  • Multipartite Viruses

Viruses that may fall into more than one of the top classes.

  • Cavity (Space filler) Viruses

Viruses that attempt to maintain a constant file size when infecting.

  • Tunneling Viruses

Viruses that try to “tunnel” under anti-virus software while infecting.

  • Camouflage Viruses

Viruses that attempt to appear as a benign program to scanners.

  • NTFS ADS Viruses

Viruses that ride on ...

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