The first mission involved finding five symbols on a Transformer breastplate. The code I got t was 7DDM7 which opened up a PDF of various Transformers CGI images (a few below). One of them included "Blackout" which is adds fuel to the argument that the gray Decepticon fighting Optimus is that character resurrected. Also note the red M&M in Barricade costume.
The second mission was finding three symbols in YouTube videos. The code after that mission was 5XYZ7. The code provided four wallpapers of various screen resolutions of Optimus Prime, Bumblebee, Starscream and Megatron along with their M&M counterpart.
The third mission is three trivia questions specific to the first movie. The code for that mission is 8TPM4. The last code provides T-Cube, a widget for the desktop that provides Transformers trivia.
The site also has a percentage that indicates the amount of "Strawberried Peanut Butter Candies" in a vault. I assume the higher the number, the more content that might become available.