If you are Using Windows XP open any folder and and click on the
and unselect the Hide Extensions of known file types.
This will release the file extension which is by default is hidden.( File extension means .txt, .jpg , .doc etc.)
By renaming the file extension ,automatically Windows Xp and most windows would not recognize the file. Even an unexperienced spy would ignore the file . Eg : renaming your secret text files that contains your credit card details to filename.mpg or filename.dll or something you like ,like filename.sky
One more cool example would be renaming your files into .zip or .rar files. The spy would try to unzip it but… its not even ZIP! haha cool huh (zip means compressed file).
This is a very weak protection but is a very good protection.There are a few ways to break this .
1) If its a video file just force load it on VLC media Player. VLC media player doesnt care what extension it uses if it is a video file with format it knows it will play it.
2) If its a text file, doesnt matter if its Microsoft .doc or .pdf you can just force open with notepad. Text file are harder to lock with this method but will make it harder to find. because any file can be open as text file and if it is in some kind of text format it can be viewed with notepad, without the formatting of course ,infact those formatting would appear like jibberish. Try opening .doc in notepad. Therefore it is safer to save your text documents in image files, using bitmaps or any image editor with text writing capabilities.Or you could take an image of your document using print screen and paste in microsoft paint.
3) load the files in Macintosh operating systems. the Mac OS doesnt use files extension systems like the windows but rather reads the header of files to identify its class.There is also away to lock this.
Besides reading extensions of files Operating System and applications also read HEADERS of the file.Usually the beginning of every files there is a header sometimes text introducing it self. Telling applications and OS what file type,size and etc. about it self. Try opening a video file with a notepad to see for yourself,but becareful not to open large files. Notepad has a file size limit. Get wordpad or other more powerful text editor and you might be able to open those larger video files. Also you could use a HEX editor. Anyway what im trying to say here is but cutting out the header of these files you would add another level of security to locking your files. These header you could save it in another file .If you want to send sensitive information then you could send this file separate from your main file.
Actually the method discussed here is not a lock Rather its a way to make your file NOT RECOGNIZABLE to your operating system and application, by taking out data that tells the computer what data it is.
There is more complexity you could add to this system, which could make it feasible to be used more generally. But i havent had the time nor the need to write up a program. 😉