Terry's Computer Tips - Newsletter
December 12, 2005

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Volume 1, Number 26 -- Monday, December 12, 2005
Part 1 | Part 2 | Part 3

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6.  Hidden File Extensions in Windows

One of Microsoft's attempts at "user friendliness" is that recent versions of Windows are set to hide file extensions. What's a file extension? As an example, it is the ".exe" that is at the end of a program's name.

Unfortunately, Microsoft decided that we don't really need to know what file extensions are. Even worse, they decided that Microsoft programs including Windows might not always consider the file extension, when deciding which program to use with a file.

Huh? That was a lot of words. Let's take it in shorter sentences.

A file extension is the ending of a file name. For example, Microsoft Word's file name is WINWORD.EXE. Word, by default, declares to Windows that it owns files with the extension ".doc". So, if you double-click on a file ending with .doc, Word will try to open it. Similarly, the Notepad program "notepad.exe" declares ownership of the .txt file extension. [By the way, Windows is not case sensitive, so it views Notepad.exe and notepad.EXE and NoTePaD.EXe as the same thing.]

Finally, by default, you do not see file extensions -- Windows hides them.

OK, so what's the problem?

The problem is that, in older versions of Windows, the period (".") was not a valid character for a file name -- it was only valid as a separator between the first part of a filename and the file's extension.

Windows XP, and I think Win2000, changed that. They joined the Linux/Unix naming conventions to an extent with that change. Now, a period is valid within the file name, or even multiple periods, in addition to the one separating the filename from the file extension.

So, you could rename WINWORD.EXE to Win.Word.2000.exe, if you wanted. It would still execute the same program. (Of course, if you did, you would have to change any Word shortcut, too, so that the shortcut still worked.)

Now, let's look at another case. Say you get an email with an attachment labelled my-neat-pictures-from-the-beach.jpg . We all know .jpg files are image files -- picture files -- so, it's safe, right?

Wrong! With the Windows defaults, which hide the file extension, the file might really be my-neat-pictures-from-the-beach.jpg.exe -- see the problem? It might really be a program.

The fix is to turn off the Windows setting "hide file extensions."

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7.  Turning Off the "Hide File Extensions" Setting

One of the first things I do on my computers is to turn off the Hide File Extensions setting. I also do this on almost every PC on which I work.

Whether you are using Windows 95, 98, Me, 2000 or XP, the technique is similar.

In Windows XP, open up Windows Explorer. Right-click on the Start button. Then, left-click on Explore.

Click on Tools, Folder Options, View.

Then, uncheck "Hide extensions for known file types."

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8.  Another security issue with file extensions

One of the other tricks in malicious emails takes advantage of file extensions. We're all familiar with web sites ending with ".com". [Yes, I know that English punctuation rules put the sentence's period inside the quotation marks, but that's confusing when we talk about computer stuff. Therefore, I ignore that punctuation rule under these circumstances.]

What would you do with an attached file that was labelled www.yahoo.com ? Click on it? It could be www.yahoo.com.exe, so you get suckered again.

If you have turned off the "hide file extensions" setting in Windows, and the file showed www.yahoo.com, do you click on it?

No. They are not common now, but ".com" is the extension for another type of executable file.

In other words, an attachment with .com is just as bad as an attachment with .exe. If you know the person and are expecting the file, you're probably ok. If not, be suspicious.

Basically, the list of file extensions that can get you in trouble, if you click on their files in an email, is long and varied. The best rule is:
"if you don't expect the email with the file, do not open the file."

If you really want to see a list, go to http://antivirus.about.com/od/securitytips/a/fileextview.htm . It will be far easier to remember the rule.

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9.  Recommend my Terry's Computer Tips Newsletter to Your Friends

If you like my  Terry's Computer Tips email newsletter or the online edition, you can help me increase the number of subscribers to my free emailed newsletter.  Recommend it to a friend.

Don't forget — the email newsletter has special Just For Subscribers articles that are available only in the email version. I also send occasional Special Edition Newsletters, too.

If you get my free Terry's Computer Tips email newsletter, please feel free to forward your copy of the newsletter to a friend or friends that you think would be interested, including all copyright notices and any advertising.

Of course, if you do not get my free email newsletter, I invite you to subscribe, too! Click to subscribe.

The current issue and the newletter archives are available online at http://www.terryscomputertips.com/archives/, and, of course, via a link from the navigation bar on each Terry's Computer Tips web page.

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9.  Send me some email!

I always have time to read emails from you -- the readers of Terry's Computer Tips.  I can not promise a personalized response, but I reply to many of the questions, tips, comments and feedback emails.  I also may use your email in my newsletter!

Send me your comments, send me your tips, send me your questions, and send me your feedback!

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Back to Part 1   Part 2

Volume 1, Number 26 -- Monday, December 12, 2005
Part 1 | Part 2 | Part 3

Copyright © 2005 Terry A. Stockdale.  All rights reserved.