Several readers are reporting UDP/3478 (STUN) traffic to Amazon AWS address 54.84.9.242.  If you "got packets" or know what it is, please share below.

Update Apr 29 19:30 UTC:

Thanks everyone for pitching in and providing packets and logs! With your help, we were able to link these requests to a project conducted by Dan Kaminsky at White Ops.  Dan provided the following explanation:

At White Ops, we've been exploring some of the more interesting corners of web browsers, and what they expose via JavaScript, to detect the presence of some of the more interesting abusers of web browsers, i.e. bots.  Turns out no matter how clever an exploit is, it tends not to teleport the attacker in front of the machine, so if you can detect automation and remote control, you can detect entire classes of otherwise unknown malware.

STUN, as part of the new WebRTC protocol stack, actually exposes certain classes of bot behavior.  People are welcome to contact me privately if they're concerned about that; if it was dangerous to users, we'd file the bugs ourself.

In general, network administrators should expect a significant increase in STUN (and UDP) traffic over the next year that will ultimately be traced to web browsers.  TCP has been a fantastic workhorse but between the rise of videoconferencing (which requires entirely different network topologies in order to provide reasonable latencies and echo cancellation) and the constant push of the web away from request/response and towards push semantics for web apps, WebRTC will likely take a position alongside other normal protocols like HTTP, DNS, etc.

There is also a discussion thread on this in the SANS ISC Forum at https://isc.sans.edu/forums/STUN+traffic/745/ and https://isc.sans.edu/forums/STUN+traffic/745/2/