What an amazing Sunday read, a step-by-step explanation, tables, timelines, even a short video demonstrating the exploit.
Looking at how big the impact could be if this was discovered elsewhere, and how meager the payout was and how little Valve seemed to be interested, I guess it's fair to say that security of millions of PC clients is not taken seriously at all. If this is how it's handled for a game that makes big $$, I wouldn't dare imagine how it is for thousands of online AA games and other low budget software that runs everyday in our computers.