So what we need is some sought of a technique where only the author of the data knows how to view the data and for others some thing else sholud be displayed.This is known as Steganography.
STEGANOGRAPHY is the art and science of writing hidden messages in such a way that no one apart from the sender and intended recipient even realizes there is a hidden message.Want more then Click Here.
Here is an example.I'm going to show how we can hide files within a image file.
1)First,make an archieve of the files you want to hide.(you require file compression softwares like Winrar or Winzip)
2)Let the name of the archieve be "hidefiles.rar".
3)Select an image file say "img. jpg".
4)Make sure that both the files("hidefiles.rar" and "img.jpg") are in same directory.Say in C:\ Drive.
5)Now,go to Start>Run>cmd and in command prompt go to "C:\" drive.
(for this just type "cd \" and hit enter).
6)Type "copy /b img.ipg+hidefiles.rar new.jpg" (without quotes).
That's it,now go to C:\ drive in Mycomputer and you will see a image file named "new.img".If you open it img.jpg will be opened but with increased size.
To View the files, right-click on "new.jpg">>open with>>choose program>>select Winrar Archieve.
Explanation:Here the copy command merges the 2files in binary mode.It doesn't even corrupt the encoded image file.