This afternoon's best mystery from the new reigning champs of brilliantly artful viral campaigns: a seemingly innocuous new update to the PC version of Valve's cult hit puzzle game Portal has turned out to be far more than anyone expected, and could be the first instance of using a three year old game itself to hint at future titles.

The update's changelog only wryly stated that Valve had "changed radio transmission frequency to comply with federal and state spectrum management regulations", causing players to note that each section of the game had been updated with a new radio object. At first glance, the new radios appeared to be the same that otherwise normally existed inside the game, which simply chirped out a samba version of the game's iconic end-theme song. Only later was it discovered that these new radios each contain a hidden audio file that's transmitted when you carry them to one particular point in each of the game's levels.

Thanks to the Steam forum's overeager detectives, we've already learned that the most perplexing of these pirate transmissions are in fact SSTV encoded photographs — the same used by shortwave operators to transmit images over the air — each watermarked with the Aperture Science logo to stem any doubt about their authenticity. Follow the ongoing investigations here, and ponder, via Shawn Elliott, in-game lore tying the Half Life universe to Portal's via a character who "is cunning enough to encrypt… photographs, coordinates, blueprints and hailing frequencies within her message."

Changed radio transmission frequency to comply with federal and state spectrum manage – Steam Users' Forums