If you want to secure important files from praying eyes, here is a very simple and extremely easy to use utility Plain Sight that allows you to hide the contents of a file with in another file.
The file is encrypted using a 256 bit algorithm which is then hidden within the target file.
The target file could be anything from a JPEG to MP3 or even a text file. So you could basically hide files in just about anything without hampering the target file.
However, to be able to extract the encrypted data, you need the unlock file that was created when encrypting the file.
Moreover, the data can also be encrypted using a password which is optional.
Plain Sight works well with Windows XP through Windows 7 and is completely clean (Check this Virustotal link). Required .NET Framework 3.5
You can download Plain Sight (515 Kb) from here.