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Common File Extensions
by Eric Kilgore
With the rampant spread of worms and viruses across the Internet, I'm frequently asked, "Should I open this attachment? How do I know if it is safe?"
I usually answer their question with a question, "What is the file extension of the attachment?" knowing the file extension of the file does not tell me if it is safe or not, but tells me what kind of file it is; allowing me to make a reasonable judgement about its relative harmfulness.
For those of you that don't know what a file extension is, here goes...
A file extension is the group of letters following the "." in a Windows file's name (example: Readme.txt "Readme" is the file name, and ".txt" is the file extension). If you look in files that are on your hard drive, you will see a wide variety of extensions at the end of file names. If you do not see any extensions, then you can go into "Folder Options" and uncheck the "Hide file extensions for known file types" checkbox.
SO WHAT'S THE POINT?
If you pay attention to what the file extensions are in computer file names, you will be more aware of what kind of files you are opening. I've made a table below that lists many common file extensions. This list is far from comprehensive, but is still useful. Many software companies try to develop their own file extensions for ease in locating and executing their own proprietary files.
Some of the extensions that you should avoid opening (if sent in an email attachment) are file types that are executable, such as: .cmd, .bat, .exe, .scr, .hta, .msi, .zap, and .zip
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Exten sion
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Generic Description
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Notes
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.ace
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Ace-Archiv
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Compressed file (similar to zip)
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.aif
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Winamp.File
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Audio file
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.aifc
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AIFFFile
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Audio file
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.aiff
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Winamp.File
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Audio file
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.ani
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Anifile
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Animation file
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.arc
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Arc-Archiv
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Compressed file (similar to zip)
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.arj
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Arj-Archiv
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Compressed file (similar to zip)
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.asf
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ASFFile
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Streaming media file
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.asp
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Asp_auto_file
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Active server page (used on the WWW)
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.avi
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Avifile
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Animation file (often used for movies)
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.bat
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Batfile
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Batch file (executes programs)
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.bkf
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Msbackupfile
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Microsoft backup file
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.bmp
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Paint.Picture
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Graphic file format (bitmap)
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.cab
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MS-Cabinet-Archiv
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Microsoft compressed file (usually for install files)
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.cda
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CDAFile
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CD-Audio file
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.chk
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Chkfile
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"Check" file (operating systems will often save to these if there are boot-up problems)
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.chm
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Chm.file
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Help file
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.com
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Comfile
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Communication file
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.cpl
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Cplfile
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Control Panel file
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.css
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CSSfile
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Cascading Style Sheet (used for Web pages)
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.csv
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Excel.CSV
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Comma seperated values (used by spreadsheets and databases)
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.dic
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Txtfile
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Dictionary file
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.dll
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Dllfile
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Dynamic Link Library (used by Windows to help programs talk with the Operating System)
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.doc
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Word.Document.8
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Document file
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.dot
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Word.Template.8
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Document template file
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.eml
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Microsoft Internet Mail Message
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email file
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.eps
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Encapsulated PostScript
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graphic file format
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.exe
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Exefile
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Executable file (these are the files that make programs start)
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.gho
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Ghost
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File that contains "mirror" images of computers
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.gif
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Giffile
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Graphic file format
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.gra
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MSGraph.Chart.5
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.grp
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MSProgramGroup
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.gst
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MSMap.Datainst.8
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.gz
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GZip-Archiv
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Compressed file
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.hhc
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Hhcfile
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.hlp
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Hlpfile
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Help file
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.hta
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Htafile
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Web page file
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.htm
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Htmlfile
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Web page file
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.html
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Htmlfile
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Web page file
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.htt
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HTTfile
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.htw
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Htmlfile
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Web page file
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.htx
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Htmlfile
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Web page file
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.ica
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WinFrameICA
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Citrix client protocol file
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.ico
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Icofile
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Icon file
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.inf
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Inffile
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Information file (usually driver information for hardware)
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.ini
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Inifile
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Initialization file (to tell programs what there default settings are)
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.iso
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ISO Image File
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File that contains "mirror" images of CDs
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.jar
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Javasoft Archiv
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Compressed Java file
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.jpeg
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Jpegfile
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Graphic file
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.jpg
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jpg file
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Graphic file
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.js
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JSFile
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JavaScript file
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.key
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Regfile
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Registry key file
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.ldb
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Access.LockFile.8
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database file
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.ldf
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SQLDBFiles
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database file
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.lha
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Lha-Archiv
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Compressed file
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.lnk
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Lnkfile
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shortcut file
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.log
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Txtfile
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Log file (for storing activity reports)
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.lzh
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Lzh-Archiv
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Compressed file
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.mdb
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Access.Application.8
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Microsoft database file
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.mde
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Access.MDEFile.8
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Microsoft database file
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.mdf
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SQLDBFiles
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Microsoft database file
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.midi
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MIDI
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MIDI music file
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.mov
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QuickTime.mov
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Multimedia (movie) file
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.mp2
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Mpegfile
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Multimedia file
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.mp2v
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Mpegfile
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Multimedia file
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.mp3
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Winamp.File
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Multimedia file
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.mp4
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MPEG 4
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Multimedia file
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.mpa
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Mpegfile
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Multimedia file
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.mpe
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Mpegfile
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Multimedia file
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.mpeg
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Mpegfile
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Multimedia file
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.mpg
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Mpegfile
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Multimedia file
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.mpv2
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Mpegfile
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Multimedia file
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.msi
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Msi.Package
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Microsoft installer file
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.nfo
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MSInfo.Document
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Information file
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.nrg
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NeroImageType
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File that contains "mirror" images of CDs
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.nrh
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NeroCDROMHybridT ype
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.pct
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QuickTime.pct
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Graphic file
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.pcx
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PCXImage.Document
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Graphic file
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.pic
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QuickTime.pic
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Graphic file
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.pict
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QuickTime.pict
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Graphic file
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.pif
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Piffile
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Package installer file
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.png
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Pngfile
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Graphic file
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.pot
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PowerPoint.Template .8
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.pps
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PowerPoint.SlideSho w.8
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.ppt
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PowerPoint.Show.8
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.prf
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Prffile
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Preference file
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.psd
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Photoshop document
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Graphic file
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.pst
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PSTFile
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Microsoft Outlook profile defintion file
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.rar
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Rar-Archiv
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Compressed file (similar to zip)
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.reg
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Regfile
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Registry file
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.rpm
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Rpm.Document
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Red Hat Package Management file
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.rtf
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Word.RTF.8
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Rich Text Format
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.scr
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Scrfile
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Screen saver file
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.shs
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ShellScrap
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.ssh2
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SecureShellFile
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.sst
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CertificateStoreFile
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.sys
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Sysfile
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Operating system file
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.tar
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Tar-Archiv
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Compressed file (similar to zip)
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.tga
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Targa file
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Graphic file
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.tif
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TIFImage.Document
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Graphic file
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.tiff
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TIFImage.Document
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Graphic file
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.ttf
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Ttffile
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TrueType font file
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.txt
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Txtfile
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Generic text file
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.url
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InternetShortcut
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.uue
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UUEncoded-Archiv
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.vsd
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Visio.Drawing.6
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.vst
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Visio.Template.6
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.vsu
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Visio.CustomUI.6
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.vsw
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Visio.Workspace.6
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.vxd
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Vxdfile
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Virtual device driver file (Win98 and previous)
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.wav
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Soundrec
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Sound file
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.wbk
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Word.Backup.8
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.wpd
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Word Perfect Document
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.wpf
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WinAce Preset File
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.wri
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Wrifile
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Generic text file
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.xls
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Excel.Sheet.8
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.xlt
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Excel.Template
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.xml
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Xmlfile
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Web page file
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.zap
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Zapfile
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Installer file
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.zip
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Zip-Archiv
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Compressed file format
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