The first one just said: "Changed radio transmission frequency to comply with federal and state spectrum management regulations". People were like, what the heck does that mean? So they played it and somebody had the idea to carry that radio around. At some point it started to crackle then emit more code. So people started scowering the game and found more. Twenty six radios that when you carry them to specific spots in the game they get reception of some sort of signal. So they recorded all the audio and began fiddling with it. The forums were going nuts, people trying to decode it. Eventually some old HAM operator had the idea to run it through a slow-scan television decoder and it produced images. Those images had all sorts of cryptic blurry stuff like keyboards and equations on paper and stuff. But people noticed the equations were slightly wrong, stuff from like wave theory and crap but slightly incorrect. So they pieced together all the inconsistencies and created a long alphanumeric string. Then some other nerd noticed that it looked like an MD5 checksum, and did a reverse checksum using an MD5 exploit. It produced a phone number in Kirkland Washington.
They call it and get what sounds like a fax machine. They talk and talk about it until somebody says "Hey, that's no fax machine, I connected with my old modem and a terminal and got an old BBS asking for a logon!".
So now they need a username and password.
Well, they keep looking for patterns and some dude notices the wave files are all encoded in this weird frequency. They took that frequency and somehow turned it into a short series of letters. Those letters they then converted using book/paper you can find in the game that one of the scientists wrote with a short encryption scheme
It gave them a username/password that let them into the BBS
It then spit out all kinds of random info from Aperture Science including ascii art.
Seriously, I guessed early on that something was up and soon after the patch was released I headed to the forums. I got to watch as all this unfolded before my eyes while I _attempted_ to study math, hahaha (FAIL)
It was like a play-by-play geek sporting event, hahaha
Insane though, I couldn't believe all the random theories people put forward and the ones that actually WORKED!!!
Valve is nuts, dude, totally nuts