"Even more, don't store credit card information on Steam: simply enter the number each time you make a purchase." Unless you're using a virtual keyboard, this is actually less secure since the exploit they're talking about is also a keylogger.
The guys at Steam could write some code identifying when the user's browser is attempting to pass the pwd2 form field (or any other unexpected form field/value pairs) when logging into Steam. This would help the users identify whether or not they have this malware running on their machine.