Before the 03 July 2014 was possible to crash, freeze and in some cases probably even executing malicious code against all the players in a server or lobby of the games that use the Steam Voip API.
Do you know those games like Grid2 and the Valve ones (HL2, L4D*, Portal*) that allow you to voice chat?
Even the same Steam client for the voice chat with the friends was vulnerable.
That's what I like of frameworks and libraries.
I created a dll injected in the game process that transformed any affected game in an exploit.
The full details are available in the following PDF:http://revuln.com/files/ReVuln_Steam_Voip_Security.pdf