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Originally Posted by Neoxter

i know, u can rename a .mp3 into .doc for example, but the above website is for the average user.

No, that's not how you break a file.
If you want to know what I mean, check my facebook or twitter profiles
http://www.facebook.com/echammas
http://www.twitter.com/Edgard_Chammas
OR EVEN THIS => http://a0.twimg.com/profile_images/1...rd_Chammas.gif (But this might crash your browser).

Nevermind all of this, the easiest way to break a file on Windows is to open it with notepad, remove a character, write it back again and then click on File -> Save
In general, you can use a hex editor.