Home > Failures, Usability and design > Hide extensions for known file types

Hide extensions for known file types

For every piece of software that communicates with human users, designers and programmers have to decide what level of technical detail they will dispense to the user. The proper approach is to make a profile of your target users and adjust the level to the technical knowledge they have. For example, if you make an IDE for computer programmers, the level can be much higher than when making an internet browser that is meant for the masses. For applications or environments that serve a wide range of users, such as operating systems for PC’s or mobile phones this is of course much harder.

One of the major mistakes Microsoft made (and still is making) in this area is the "Hide extensions for known file types" option in the Windows Explorer. When this is on (which is so by default), users don’t see extensions for files for which an application is registered to handle it. For example, "MyFile.txt" becomes "MyFile" because notepad is registered to open the file when you double-click it. I understand the basic reasoning about this; file name extensions are a technical means and the acronyms like .exe and .gif don’t mean anything to the non technical user, right?

Wrong. File name extensions are a vital part of file recognition and everyone who uses Windows has to deal with them. Most non technical users know that a .jpg or a .bmp is a picture and a .doc is a Microsoft Word document.

Hide Extensions for known file types

Most will even know that a .exe or .com is something that you can start. There are plenty of applications that can save in different formats (by letting the user choose the format and extension), so they are not out of the scope of users at all. Everyone who ever received a .docx (the Microsoft Word 2007 document format) while having an older Office version will agree.

In their effort to make Windows more user-friendly, Microsoft apparently thought differently and included the "Hide extensions for known file types" in Windows 95 and after and even turned it on by default. Big mistake.

The first thing that is wrong with it, is that file names -including the extension- are used to distinguish items on the file system. Even for non-technical users. With this option turned on, "MyFile.txt" and "MyFile.exe" become the same "MyFile", distinguishable only by their different icon (and we all know icons are never self explaining, right?) So, this is likely to confuse users more than showing the complete name with extension.

But far worse, it causes great security risks. An executable file (say, an .exe) can be named .jpg.exe and Windows will hide the last part, displaying it as an .jpg. If you mail this to someone, he/she might think to have received a harmless picture while in fact it is an executable. Double-click and whoops…  In fact, many viruses used this simple trick (remember the 2001 outbreak of the "Anna Kournikova virus"?)

You would have thought that with the double name inconvenience and the security risks "Hide extensions for known file types" creates, Microsoft would have at least turned if off by default. But no, even in Windows 7 it is on. Several security companies (like F-Secure and CERT) have voiced their opinion about this but Microsoft did not change its viewpoint. Instead, they made it impossible to send executable files via their Outlook e-mail client (like that is solving anything; it only annoys Outlook users who have to send regular executables to each other while not preventing anything because Outlook is not the only e-mail client in the world).

The first thing I do on every new Windows Install I lay my hands on is to turn "Hide extensions for known file types" off. I strongly recommend you do too. If you don’t, try explaining to your mother if a file she got sent or downloaded is safe to open or not when she can’t see the extension. Good luck describing the icon over the phone.

  1. May 8, 2013 at 2:18 am

    I get pleasure from, lead to I found just what I used to be taking a look
    for. You have ended my 4 day long hunt! God Bless you man.
    Have a great day. Bye

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