If you haven't noticed, there was a sudden, mysterious update to Portal today with only one description:
Changed radio transmission frequency to comply with federal and state spectrum management regulations.A new achievement also appeared with it simply titled "Transmission Complete" with a description of "...?"
What changed is simply this: there are now 26 radios hidden throughout the game. Each one has a signal location tied to it where if you take the radio to the location you hear a strange broadcast and unlock 1/26th of the achievement.
4 of them were in morse code and read:
INTERIOR TRANSMISSION ACTIVE EXTERNAL DATA LINE ACTIVE MESSAGE DIGEST ACTIVE
9E107D9D372BB6826BD81D3542AV19D6 (which is MD5 hash for "The quick brown fox jumps over the lazy dog")
SYSTEM DATA DUMP ACTIVE USER BACKUP ACTIVE PASSWORD BACKUP ACTIVE
BEEP BEEEEP BEEP BEEP BEEEEP BEEEEP BEEEEP BEEP BEEEEP BEEP BEEP (which is, in turn, morse code for LOL)
The remaining 22 were weird whining noises. These were encrypted images. Some of them were simple images of disturbing things, a human skull, the valve guy, a view through a sniper scope. Some of them were pieces of paper with a BBS number scribbled out.
The rest were divided into 4 and numbered.When spelled out, you get 9459C6CAC8C203B8128B7CC63068D4FD, which is MD5 hash for a phone number: (425) 822-5251. This phone number is in Kirkland, Washington, where Valve began. Trying it with the other pictures, it was figured to be a BBS number.
And here is where the search has ended.
EDIT: And just now someone figured out the username/password:
An ASCII GLaDOS?
Basically, the assumption is that Valve is announcing Portal 2 and maybe HL: Episode 3 in the most badass way possible.