Advice from me for now:

1) DO NOT PLAY @TeamFortress RIGHT NOW, THERE'S SOME RCE EXPLOITS IN THE ENGINE THAT COULD ALLOW MALICIOUS CODE TO RUN RIGHT NOW

2) Be wary of what you do atm, until there's any official response from Valve, take everything with a grain of salt.

RCE exploit's for @TeamFortress are already coming out... (blurred a homophobic slur)

Here's a clip going around, that Command Prompt should NEVER open up at all.

Look at my latest tweets before commenting on this.