All of these keys unlock the page at http://www.presskillswitch.com/changethispart/.
This was from the Base-64 encoded JPG picture found in a HTML comment.
This was from the evacuation map overlay.
This was from the flipped overlay of the Porter articles and the banner from the Alterplex website.
This was from the audio clips.
Decoded: “IF YOU CRACKED THIS CODE THE FIFTH KEY IS WITHIN REACH. REQUIRED ARE THE FIRST LETTERS OF THE FOLLOWING ROWS OFTHE SOURCE CODE ON THE PAGE LAKN ALTERPLEX ENERGY PAGE. ROW FOUR EIGHT FIFTEEN SIXTEEN TWENTTHREE FOURTYTWO.”