Hidden File Extensions – Windows 7 continues the Security Risk
By on May 10th, 2009

In an attempt to make your desktop look clean and more user friendly, Microsoft had decided to hide the file extensions by default a long way back. This means that if” a file is named as sample.doc, you will see the name as “sample”, and the extension .exe will remain hidden. But the OS knows that it is actually a Word file, and therefore will open it through Word, when you double click it.

Similarly, if the actual name of a file is samplesoftware.exe, widows will show the file name as “samplesoftware” only, but it knows that it is an application and will execute it, when you double click on the filename.

So far, so good. This is a good feature from usability point of view.

But, this is also a big security risk, which has been exploited by some of the biggest malware threats like ILOVEYOU.

The issue is that several years ago, Microsoft has allowed the use of .as a valid character for filenames. This means that you can also name the same file as samplesoftware.jpg.exe or samplesoftware.doc.exe or samplesoftware.xls.exe. Windows will identify it correctly as an application, but will show the file name as samplesoftware.jpg or samplesoftware.doc or samplesoftware.xls. When an average user look it, he might innocently think that it is an Image / Word / Excel file and open it.

Malware artists have been using it for long. They can send a file attachment to you with the name my_nude_pics.jpg.exe, with a virus attached to it waiting to get activated as soon as the file is execeuted. Innocent users see it as my_nude_pics.jpg. Out of curiosity they open it, just to find that they have already executed a virus or malware file on their system.

This issue was known to Microsoft long back, but it is surprising to note that this issue continues in the latest flagship OS, i.e.Windows 7. May be that Microsoft as decided to give Readabilty a preference over Security.

How to see the hidden file extensions

You can change the default Windows settings to see the hidden file extensions. I have used that feature in Windows XP and Windows Vista. But not yet tried in Windows 7.

Just go to Control Panel, Open Folder Options window.

Deselect the check box, which says Hide Extensions for known File Types. Save your settings.

hidden-file-extensions

This might solve the issue related to many common file types but there are executable extensions that will STILL be hidden even if you turn the option off. For example PIF, which is meant to be a shortcut to old MS-DOS programs. Problem is, you can rename any modern Windows Executable to .PIF and it will happily run when double-clicked.

[This is a guest post by Silki Garg. She advises on spyware removal, online threats and malware detection, on her Internet Security Blog. A visit to her Blog is highly recommended. You're sure to find something of interest.]

Author: Silki
I am Silki Garg, a telecom professional from the holy city of Varanasi in India. I have a natural crush for Technology and having bitten by Blogging Bug. I usually have a contrarian approach.

Silki has written and can be contacted at silki@techie-buzz.com.

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