Microsoft created the ability to hide known file extensions so that everyday users would not need to be bothered with too much technical stuff.The icon associated with the file type would show you what sort of file it was so there was no need to inundate users with technical jargon like EXE or VBS or DOC or HTM.
It didn’t take long for virus writers and developers of other malware to figure out that you can add more than one extension at the end of the file name and that the last one will be hidden. So a file like mynotes.txt could be replaced with a malicious executable program called mynotes.txt.vbs, and with the file extensions being hidden it would still appear as mynotes.txt.
There are two things to note here. One, an observant user might detect the fact that only the malicious file shows any file extension at all. Using the double file extension hides the true file extension, but it still shows a file extension which gives away the fact that something is different.Two, the hidden file extensions only work in Windows Explorer. If you view the files using the dir command at a command prompt window, it will show the complete file name, including both file extensions.
Even with those caveats in mind, though, it is best to simply disable this feature so that any and all file extensions are readily visible.To disable the hiding of file extensions, go into Windows Explorer (Start | All Programs | Accessories | Windows Explorer) and select Tools, and then Folder Options. Click the View tab and uncheck the box titled Hide extensions for known file types (see Figure 1.7). All that was hidden shall now be revealed unto you, or at least the file extensions of the files on your computer system.
Click Tools on the Menu Bar in Windows Explorer and Choose Folder Options to Disable the Hiding of File Extensions in Windows.
