The Hidden Danger of Hidden File Extensions

By Yohanes Aristianto

- Why your computer is infected with spyware, adware, malware, virus, trojans, worms, keyloggers, dialers, and so on...
- Unwanted pop-ups, slow-loading web pages, degrading performance...
- Or worse: stolen passwords, credit card numbers, emails, private documents, etc.

There are two main sources of spyware and virus:
1. Malicious [components of] web pages
2. YOU executed the virus on your Windows system

Microsoft's ActiveX technology and browser flaws have made it easy for virus and spyware makers to install their malicious software into your computer. You open some web pages, accept a security warning, and then... you are in big trouble. To prevent this from happening, the easiest way is to use another browser (Internet Explorer has a large user base, so there are many exploits for IE). Use an alternative web browser like Opera or Firefox:

In this short tutorial I will focus on the second source of spyware, virus, and other nasty threats:

Without Knowing It, You May Execute a Malicious Software on Your Computer

Yes it is true. The spyware is installed in your computer because YOU installed it.
Of course you won't be that stupid to open any of these files:

  You recognize their ICONS:
You know they are applications, they are computer programs, they may harm your computer.

And how about these? Would you try to open them?
Just double-click. Are you not curious? It costs nothing to try!


You also recognize their ICONS:
You know they are a ZIP file, a folder, and a text file.
You think it is safe to open them. (a folder is never a virus)

But... have you ever thought... that the above files might be some viruses in disguise?

It is possible to disguise a computer program as a "folder" simply by changing the program's icon. A programmer can use any icon for his program. This means he can choose a Windows folder icon (or text file icon, ZIP file icon, etc.) for his program. Once executed, this seemingly harmless program can do anything: it can record your keystrokes, log your activities, display random pop-up windows, slow down your computer, and so on.

Why did you open these malicious programs in the first place? Simply because they have some interesting names and you recognized their icons; you thought it's safe to open them. The case would be different if this is what you see:


Most likely you will notice the .exe file extension.
You know .exe is the file extension for applications.
Unknown applications are dangerous; you won't open them.

What is a "file extension"?
It is the one or several characters at the end of a filename. For example, if you have a file MY LETTER.TXT, the file extension is TXT, and it indicates the file can be opened with Notepad. Of course you have heard of MP3, JPG, ZIP, MPEG, EXE, ... They are all file extensions.
Common file extensions for applications are EXE, COM, and BAT.
You should not open files with suspicious extensions.

The Solution: Show File Extensions

File extensions are hidden by default, so you have to unhide the file extensions.

Open Windows Explorer, click Tools — Folder Options...

In the Folder Options windows, click the "View" tab and unmark the option "Hide extensions for known file types". Click OK.

You are done!
Now you can see the file extensions and won't be vulnerable to the cheap trick explained above.

Other ways to keep your computer safe, or specifically, to protect your privacy:
- KL-Detector: my free key logger detector
- I Hate Keyloggers: my commercial anti-keylogger (please buy it to support me)

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