How to show filename extensions in Windows

Windows is designed to be user-friendly, to the point where filename extensions (the bit of the filename that Windows uses to decide which program should open a file) are by default hidden.

This can have serious repercussions, where some viruses attempt to disguise themselves as an innocuous spreadsheet or word document. Double clicking on the filename does not open Word or Excel as expected, but executes the virus.

There is a simple way to ensure that filename extensions are shown however;

Double click on My Computer from the Windows Start menu. (You can use any method for launching Explorer.)

Choose Folder Options from the Tools menu. Then, click the View tab.

In the Folder Options dialog box, uncheck the Hide Extensions for Known File Types option.

Click OK.

Now when you view filenames, you can see exactly what sort of file you are about to open.