It's worth noting that a vulnerability was recently-ish found in GNU's ZRTPCPP library. That's the library that handles the encryption for Silent Circle's app... I don't think Open Whisper's RedPhone uses it, but frankly I never really bothered looking at what it uses...Anyway, if you're using old versions of a voice encryption application, you probably want to update if there's something newer available -- that or make sure your app of choice isn't using a version of ZRTPCPP that's vulnerable.It isn't the encryption that's the problem, BTW. Apparently it's possible for unauthenticated remote attackers to execute arbitrary code.