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Show Your File Extensions To Avoid Malware

A common tactic with malware involves a file naming scheme.

By default, Windows hides file extensions of known file types. A file will show as “Resume” for example. If this is a Word document, it will display a Microsoft Word icon. If it’s a PDF file, it will display an Adobe icon. The icon displayed, and the program needed to open it, are determined by the file extension. In the days of DOS, file extensions were a period followed by one to three characters. For example, the file IO.SYS has a .SYS file extension. Since then, file naming rules have changed. One of the changes allows longer file extensions, like .TIFF and multiple file extensions, like IO.SYS.OLD for example. In this case, the file extension is just .OLD – not .SYS.OLD.

Malware takes advantage of hidden file names and attempts to fool you into opening a file. For instance, if you get an e-mail with an attachment called “RESUME.PDF”, you might open that attachment. However, if your file extensions are hidden, the attachment may actually be named RESUME.PDF.EXE and is a malicious executable file rather than an Adobe document. If you saw the complete file name, hopefully you would think twice before opening it.

Open File Explorer and across the top, it lists “File, Computer and View”. Click View. Click Options.

Picture of settings to avoid malware


Uncheck “Hide extensions of known file types”.

When you do this, you’ll see that a file named “My Document” now shows the complete file name “My Document.docx”.

If you show file extensions, you are less likely to be fooled by these tactics.  Use this tip to protect your data!  Good luck, and take care!

We welcome your suggestions and questions.  Please contact us anytime!


p.s.  Hope you’ll follow us on Facebook…

14 Jan 2021: Post updated to include links to new company pages on Social Networks.

Mark Mullarky

President, Great Lakes Tech Services, LLC
Organizer, Wisconsin Business Owners

2607 N Grandview Blvd Suite 160E
Waukesha, WI 53188
Phone: 262.720.3668

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