KLTA Web Tutorial

What Kind of File is That?

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Your computer is a very complex machine, with thousands of files residing on your hard drive that do things from run the software that shows images on the screen to displaying web pages and writing letters in Microsoft Word. Each of these files has what's called a "file type" that tells Windows what to do with it when you want to open or use the file. There are a few kinds of files that you'll come across in your web meanderings, which we'll cover here, and thousands more that we'll give you some resources to help you look up in case you run across them and need to know what to do.

The most common web file types:

This is an incomplete list of the file types you're most likely to see on the web. It is by no means a comprehensive list.

Not to scare you, but some file types are more likely to carry viruses and spyware than others. These have been highlighted Red and will have a short explanation as to why they are sometimes problematic for Internet users.

  • .AVI
    Windows video clip multimedia file. This file will usually open in Windows Media Player.

  •  .BMP
    Windows BitMAP image file. This file will usually open in an image editing or Windows preview program.

  • .DOC
    Microsoft Word Document file.
    This file will only open in Microsoft Word. If someone sends you a .doc file and Microsoft Word is not installed on the computer you are using, you will usually have to request that the person send it in another file type that can be read by more generic programs, such as Notepad or Wordpad, which are installed by default on Microsoft Windows. The more universal file types are Plain Text (.txt) and Rich Text Format (.rtf). Word documents can also carry annoying viruses, so make sure that you have AntiVirus software installed on your computer. Most public computers already have this software installed.

  •  .EXE
    Executable program file.
    This kind of file will run a program on your computer. You want to be very careful when dealing with .exe files, as they can easily contain viruses. The key point here is to know and trust your distributor, and NEVER run a .exe that is attached to an e-mail message. Here again, having current AntiVirus software installed on your computer will help a lot, but is no guarantee. Just be careful around .exe's.

  • .GIF
    Graphics Interchange Format image file. This kind of file is a standard Internet image file. They are often the kind of image files that are shown on web pages, and if saved will open in your image editing or Windows preview program.

  • .HTM, .HTML
    HyperText Markup Language file. This kind of file holds the information your web browser (like Internet Explorer) needs to display a web page on your screen. The document you are viewing right now is an .HTM file.

  • .JPG, .JPEG
    Joint Photographic Experts Group image file. JPEG (pronounced jay-peg) files are also standard Internet image files. They are also often the type of images produced by digital cameras when you save your digital pictures to your computer. JPEG's will open in your image editing software or Windows preview.

  •  .MOV, .QT
    QuickTime MOVie multimedia file.
    This kind of file will only open with the Quicktime plugin (available from this website) from Apple. Once you have the Quicktime program installed, you will be able to view .MOV and .QT files with ease. Most public computers already have Quicktime installed.

  • .MPG, .MPEG, .MP2, .MP3
    Moving Picture Experts Group multimedia file. These kinds of files will work in almost any media player, including the Windows Media Player, Quicktime, and many others. These are media files that can contain video (.MPG, .MPEG) or audio (.MP2, .MP3). MP3 files are very popular for sharing music online due to their small size and relatively high quality.

  • .PIF
    Program Information File. Never, ever open one of these. Nine times out of ten it will be a virus that will immediately scan your computer for e-mail addresses and send the virus to all addresses it finds. Just say no!

  • .PDF
    Adobe Acrobat Portable Document File.
    These files will only open if the Acrobat Reader software is installed on your computer. Please see these instructions if you cannot view a .PDF file.

  • .RTF, .TXT
    Rich Text Format document file, Plain Text document file. These files are the most compatible types of text document files. They will open in almost any text editor (such as Notepad or Wordpad on Windows, TextEdit on Mac). When sending documents to friends, minimize frustration and save your document as one of these in case they don't have Word.

  • .SCR
    Screen Saver file.
    Here again, if it comes in your e-mail, don't open it, it is most likely a virus. Screen savers are cool, but viruses aren't, and you most likely didn't request to receive a screen saver by e-mail, so don't open them. Consult your local geek if you have questions.

  • .WAV
    Wave sound file. These files are sound files, and will open with almost any media player, such as Windows Media Player, Quicktime, and many others.

  • .ZIP
    PKZIP compressed file
    . These files require either Windows XP or the WinZip program (available at this website). The "zip" means that the file is compressed, or "zipped" up to make it smaller and quicker for you to download. Zip files are often used over e-mail, but be very careful as these files can also carry viruses. Make sure that you have up-to-date AntiVirus and never open a zip file you weren't expecting. It's best to err on the side of caution.

  • See a file that you can't identify here? See this site for more information.

A final word about Internet Safety

Just like a city with lots of people and activities of all concieveable natures, the Internet can benefit us and enrich our lives, but we still need to be careful about where we go and what we do. Just like being aware of your surroundings in a bad neighborhood, we need to be aware that there are people out there using the Internet who do not have the most wholesome of intentions, and if we're not careful, we can become targets for their schemes. Here's a few tips on how to protect yourself online.

Protect yourself online
  1. Be able to recognize a scam. If you plan to use the Internet at all for your business, personal or social needs, save yourself a lot of time and energy by knowing the different types of scams out there so you can bypass them altogether.

    These sites might help you get educated about scams online:
    Site Seeing on the Internet (from the Federal Trade Commission)
    Internet Scam Busters

    US Department of Justice Criminal Division Fraud Section

  2. Never reply to any message advertising a fraudulent scheme.

  3. Use your Internet e-mail service to block junk or 'spam' e-mails. Check your online service for ways to reduce unsolicited commercial e-mail. Yahoo! mail does do spam filtering.
    Information regarding Yahoo! e-mail spam filtering.

  4. Never download an e-mail attachment from an unknown sender. It could be a virus.

  5. Don’t respond to any e-mail that asks for money up front.

  6. If an offer is too good to be true, it probably is.

  7. Understand that nobody is on the Internet with the sole purpose of making you rich.

  8. Investigate Internet-related business opportunities just as you would investigate any business opportunity.

If you follow these general guidelines, your online life will be just as safe and secure as your offline life. Treat solicitations in e-mail the same way you would treat solicitations in the US mail, trash them and forget them.

Protecting your Privacy Online

When you sign up for a free Internet service (such as Yahoo! mail or eBay) be sure to read and understand the privacy policy of that company. Most mainstream companies promise to not sell your personal information, but there are still some who do.

The KU Information Technology Security Office has some excellent tips on how to protect your privacy online.


You are now ready to explore and enjoy the web safely and securely.

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Page last modified: January 10, 2008

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