Unless you tell it otherwise, Windows hides the important part of a filename, the extension. I guess Microsoft does that so as not to confuse to bewilder beginners, though in my opinion it merely reinforces the fault in default.

A filename has two basic parts: the name and then the extension. The extension begins with a period and then typically three more characters, though an extension can be anywhere from one to four characters. For example:

railroads.doc

The filename is railroads, the extension is doc. That doc extension identifies the file as a document file, belonging to a word processor. In the Windows world, that normally means the Microsoft Word word processor; doc is a Microsoft Word document.

wambooli.html

The html extension identifies a web page document, though the letters htm are also acceptable.

playtime.exe

The exe filename extension is used in Windows to identify program files, and that’s where the problem lies. It’s possible for the Bad Guys to disguise a virus or other malware to take advantage of the fact that Windows normally hides the filename extension. For example:

evilprorgram.doc.exe

The filename is evilprogram.doc and the extension is exe. Yep, you can use a dot, or period, in a filename. It’s only the final dot and the characters that follow that Windows recognizes as the filename extension. So on a typical Windows PC, the kind configured by Microsoft as it comes out of the box, the above file looks like this:

evilprogram.doc

which appears to be simply a Microsoft Word document. A user may just open that file because it looks harmless.

The sad news about all this is that only now — some 14 years after the problem first appeared in Windows 95 — is Microsoft admitting to the problem.

The fix is to recajigger Windows to always show filename extensions. Here’s how:

1. Press Win+E to open a Windows Explorer window.
2. In Windows Vista, press F10 to show the hidden menu bar.
3. Choose Tools > Folder Options.
4. In the Folder Options dialog box, click the View tab.
5. Remove the check mark by the item, “Hide extensions for known file types.”
6. Click OK.

After following the above steps, Windows will always show a full filename. Sure, a beginner might be frightened and run screaming from that change. The truth, however, is that a computer is a complex machine. Understanding a simple concept like filename extensions makes you a better user and keeps your computer safe from the Bad Guys. Make the change now, if you haven’t already.