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The FBI issued a warning regarding hotel Wi-Fi access points, and any other public access point.

I'd like to make sure my apple device always uses a VPN when using Wi-Fi. That way even if an attacker were to see my data, they would only see an encrypted jumble of bits. Note that this hack can also be applied to HTTPS connections.

How do I ensure that OSX automatically uses a VPN when using Wi-Fi?

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Are you asking how to automatically start a VPN session when you connect to a wifi access point? You should clarify this. – zwerdlds Apr 26 '13 at 15:21
It would be interesting to see progress on the part where the <At least if "goes over the VPN" is something that iptables can see> part of the proposed solution is lacking in details. – bmike Oct 8 '13 at 13:14

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You can not ensure all traffic is protected. You also can't easily block traffic while waiting for VPN to connect, authenticate and secure without having two OS running:

VPN requires an open Wi-Fi connection to be built before it can reach out over that open/hostile/insecure Wi-Fi connection to secure a limited portion of the traffic leaving your Mac.

In other words, you have asked how to only drive on a freeway from your garage without using the driveway or surface streets. Once you're on the freeway, you can stay on it and not get off, but you need the streets to get there in the first place. Worse, VPN only obscures the windows of your car so things that are packed inside have some more expectation of privacy from casual observers.

On a practical level, you can set your Wi-Fi to never save a joined network or meticulously set then to never Auto-Join so you have control over each and every untrusted Wi-Fi connection and can ensure no apps are broadcasting before the VPN tunnel is established.

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I believe the OP is asking how to automatically connect to a VPN after joining a (public) wifi. – Gerry Oct 4 '12 at 15:28
@Gerry Let's see - you can always try editing the question into shape to sharpen it (or answer based on that assumption) - Part of this process is the community shaping things. I thought it was a "i know what I want and it's X" but I could easily be wrong or mistaken. – bmike Oct 4 '12 at 15:31
→ bmike: very nice image! During my last waiting time in an airport I observed what was going before I was even connected to anything. That was a real traffic jam of broadcast attacks (automatic) on the netbios range of ports. A tcpdump showed me a real nightmare, and I could only guess the number of (unaware) sniffers on all the PC around me. I support your clear explanation that there is an insecure world between the Wi-Fi connection and the VPN building. – daniel Azuelos Oct 8 '13 at 6:40

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