What does "If you change a file name extension, the file may become unusable" mean?

The idea is obviously to make file management idiot-proof, but it really makes a lot of sense to learn how to recognise and use file extensions. I automatically unhide them on Windows installations. Vista took a step in the right direction by only highlighting the actual file name when renaming.

I found this article to be very informative . It has given me very good information.I had no idea how to make the changes you have just shown.

I have file extensions showing, as it may show up a rogue .exe masquerading as something else.

I use this site when I run across an extension that I don't know which program it belongs to. It also helps when checking the default file associations, especially after a new piece of software starts changing those associations. There are other sites out there that do the same thing, but this one suits me the best.

http://filext.com/index.php

R

Finally you have solved my identical problem which I have been having with file name changing and receiving the same dialog box. Thanks ever so much.

For this and the related 3 articles I will buy you a coffee.
The articles solve many problems I have had over time and still get once in a while.
Thanks again Leo

Thanks for that info... I learned something today! Now why those little pesky things pops up makes sense! I had no idea how to fix it.

Would this be a backdoor way to make a file inaccessible to someone else? Say I have a journal I keep in Word but don't want anyone else to read it. Can I simply to to Explorer after saving it, take off the .doc extension, then, when I want to open it, go to Explorer, edit the filename to add the .doc? Would this hurt the file any after doing it several times?

It won't hurt the file, but it could be discovered if someone went looking. "Security by Obscurity" is rarely a truly secure approach. If it's important, encrypt it.

18-Aug-2009

@Alexis Corelis -- For a personal journal? ...Maybe -- and that's assuming whoever wanted to read it had to find it first and was not particularly computer-savvy.

But for anything even slightly more important than that, changing the file extension is more likely to be completely ineffective.

Even on Windows, it's trivial to detect the type of most commonly-encountered files even if the extension part of their filename is missing or corrupted: all one has to do is open the file and try to recognize what's in it -- in many cases, this is as simple as reading the first couple of characters. For instance, an .exe file (or a .dll, for that matter) can be recognized from its first two characters: "MZ". A .zip file will start with "PK". Linux ELF binaries all start with the characters "ELF". All of these are part of the standard that defines how these files are created and used, which means there are very well-known signs to watch for when trying to find out what type a file is.

The main reason against detecting a file type this way (and thus making the extension irrelevant as a way of actually determining a file type) is that opening, say, 1,000 files in the same directory in order to read the first few characters in them is a slow process. Nonetheless, I'm vaguely certain Linuxes (and probably Mac OS X) have been doing it for a while now. On my Xubuntu, I can rename "my-pic.png" to "hahaha" and it still gets properly detected as a PNG image and opens correctly if I double-click it. Note that this is something I can do without any work on my behalf at all -- it's part of the OS itself. And I'm certain the same capability could be built into Windows, at some potential (small) cost in speed.

To summarize: an extension is just part of a file name, which is why it's not likely to be particularly trusted as anything but a first guess at what might be inside. As such, renaming a file to hide its extension does not make it any more secure than moving it into the recycle bin and moving it back out when you want to work on it.

If you have any type of data you truly consider sensitive, use some kind of encryption to hide it behind a password or passphrase only you know. Leo has been recommending TrueCrypt for a good long while, and with good reason.

@R: You could also try http://dotwhat.net/ which is pretty useful, thanks for the tip though.

To post a comment on "What does "If you change a file name extension, the file may become unusable" mean?", please return to that article's main page.