The hidden content is linked to a new PC Achievement “Transmission Received.” To hear these secret messages, players have to position new and old radios around various challenge rooms, at which point you’re bombarded with up to twenty-six different Morse code messages.
Tantalisingly, the full coded information has yet to be fully cracked. What we have so far, however, is:
“Interior transmission active
External data line active
Message digest active
System data dump active
User back up active
Password back up active.”
All this suggests GlaDOS is very much up to her old tricks and will be back for the oft-rumoured sequel. You can also check out the source article for some encoded screens which can be found in the intriguing update.