The old one got really derailed, PLEASE don't let this thread get derailed like the previous one. PLEASE!
Back on track, the last topics I covered in computer security are if you have any personal info you don't want hackers getting, you can RAR it and put it in a picture file. Also if you have any files to get rid of that have personal info, don't do a standard delete, instead download Eraser and and use that to wipe out the info completely on 35 pass Gutmann erasure setting.
Next topic, encryption. Simple encryption can be achieved with a simple visual basic program that XORs each byte of data with a random value, and then storing all the random values in a key file. You need the key file to decrypt the encrypted data in order to retrieve the original data.
Also picture in picture steganography is useful. For example, take a picture you want to hide in another picture and convert it to a dithered combination of the 8 possible 3bit colors (1 bit per channel instead of 8 bits per channel). while taking the container image and removing the lowest bit of data from each color channel. Then take the 1 bit per channel image and insert it into the lowest bit plane of the 8 bits per channel image. Now you have 2 pictures in one. To see the hidden picture, just extract the lowest bit plane of the 8 bit per channel image and display it as a 1 bit per channel image and you'll now see the picture that was embedded invisibly in the main picture.
However this technique is easy to detect using the simple histogram in Photoshop, and to remove the hidden image just do the SLIGHTEST possible blur and it completely obliterates the lowest bit plane of the container image, turning that bit plane into random noise.