This steganography software inserts data in the image file in a random way depending on a key (which is also used to encrypt the data), and changes other bits of the image file to compensate for the modifications induced by the hidden data so as to avoid modifying statistical properties of the image file. It is thus more secure than most steganography programs.
Stego PNG has a simple user interface and is easy to use. Here is a typical screenshot, after hiding a file: