You might have noticed Steam downloading an update for Portal and HL2 Episode 2 earlier. Just a routine patch, you probably thought. You're wrong, stupid! Learn to be more paranoid, why don't you? Important secrets are being revealed...
The update details said, simply, "Changed radio transmission frequency to comply with federal and state spectrum management regulations", which sounded like some obscure audio fix to kowtow to some obscure health and safety law. It's not. In fact, it's a series of secret messages, which are activated by carrying an in-game radio to several in-game locations. Which is in itself a compelling and playful mystery, especially as the sounds played at those locations wibbled on about transmissions and data dumps - y'know, computery talk. Like, say, from a murderous AI that's awakening again. Maybe. That's only the half of it, though.
Terrifyingly industrious members of the Steam forum have ascertained that some of the sound files contain hidden images, visible when run through a Slow Scan Television (SSTV) application. There's a growing list of links to the revealed images here - but all they serve to do is further the mystery. Equations, skulls, keyboard buttons - and, most tellingly, the Aperture Science logo. Expect further developments as this ingenious ARG continues to run its strange course, which is being documented in realtime here. Oh, that Valve lot really are clever bastards.
I'm quite sure Ie'll wake up to yet more revelations tomorrow - but to what ultimate end? The smart money's on a Portal sequel, of course, but it could be something else - or something more. For instance, this extra radio transmission:
Is that GLADOS saying 'get out'? And is that gunfire in the background? Combine gunfire, perhaps?
Your field day. Go have it.