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I am aware that 'hiding' a wifi network/SSID does not make the network MORE secure, but Apple's warning on IOS 10:

Using a hidden network can expose personally identifiable information

seems to indicate that hidden networks are LESS secure.

Clicking the 'learn more' link does not give any further info supporting the claim.

Exactly how can hiding an SSID make the network any LESS secure (by "expose[ing] personally identifiable information")

IOS 10 hidden wifi warning

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up vote 9 down vote accepted

Clients that connect to known networks automatically will advertise “hidden” SSIDs in all of their probe requests. This results in your device broadcasting those SSIDs everywhere you go, to anyone who’s listening.

This behavior is dependent on the client’s operating system. For instance, you can configure Windows 7 and later to not connect to hidden networks automatically (only “visible” ones). That prevents such broadcasts from happening, but then you have to connect to hidden networks manually every time.

On the other hand, iOS (and presumably macOS) always connects to known networks, hidden or not, and therefore broadcasts hidden SSIDs. The fact that iOS 10 warns about this would indicate that Apple has no plans to add the kind of toggle switch that Microsoft added in Windows 7, or to force the user to connect manually.

Microsoft explains this behavior on TechNet:

A non-broadcast network is not undetectable. Non-broadcast networks are advertised in the probe requests sent out by wireless clients and in the responses to the probe requests sent by wireless APs. Unlike broadcast networks, wireless clients running Windows XP with Service Pack 2 or Windows Server® 2003 with Service Pack 1 that are configured to connect to non-broadcast networks are constantly disclosing the SSID of those networks, even when those networks are not in range.

Therefore, using non-broadcast networks compromises the privacy of the wireless network configuration of a Windows XP or Windows Server 2003-based wireless client because it is periodically disclosing its set of preferred non-broadcast wireless networks.

Now as to why this is a privacy issue:

  1. You are potentially revealing SSIDs to a lot of people. Those SSIDs may include first and/or last names, which I’ve seen people use in network names.
  2. Should I point out the irony of broadcasting an SSID in the direct vicinity of the access point trying to hide it?
  3. Someone with a database of SSIDs could figure out where you’ve been or where you spend your time—possibly even where you live and work, based on your SSID broadcast beacons. Knowing where you live and work could lead to figuring out who you are, or at least identify you among a group of wireless clients (since your broadcasts might be unique to you).

Sound far-fetched? Criminals/advertisers have done worse things. Thankfully, no one I know has used a hidden SSID in well over a decade, and I haven’t seen that practice recommended in about as long.

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Ok, so i can see how, perhaps, a CLIENT, by broadcasting the 'hidden' SSID when out of range of it, might disclose "personally identifiable information" (the SSID). But does this mean that hidden networks CANNOT be connected to automatically, WITHOUT the client broadcasting the SSID? – goofology Jun 28 at 21:56
    
That is correct. – Phong Jun 28 at 23:03
    
If the network is not hidden, does that mean that its SSID will not be broadcast in probe requests? I'm not sure I see why this is less and not at least equally secure as a visible network. – tedmiston Sep 19 at 7:28

Preface

I think what Apple's message on your screenshot wanted to say is that hiding networks' SSID won't allow them to hid anything except that. So basically they're telling you hiding networks isn't safer it just doesn't broadcast the SSID.

I agree with you the message can be very tricky to interpret, but I see this as the only reasonable way to read that. But let's not desperate, it's still a Beta, Apple changes a lot in Beta versions, so hopefully they'll update and clarify this message as well!


Thus, as Apple wrote on that page it suggested you:

Hiding a network doesn't secure your Wi-Fi network, because the SSID is still available through other mechanisms. Security is enforced by a different setting.



End of the story

Hiding networks' SSID won't make them safer or more secure.

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2  
This is not at all what Appleis saying. – samh Jun 29 at 15:56

Since iOS 10 all of a sudden our iOS devices seem to forget the hidden SSIDs quite often. So I already wondered whether there is a bug and Apples explanation that hidden SSIDs aren't totally secure anyway just should prevent this bug from happening. I'd still argue that a hidden SSID is broadcasted as any other SSID so only if I make the mistake to name my hidden SSID naively it can cause any trouble. Otherwise I would say that any person in vicinity who sees my SSID gives it a try to find the password (it's unlikely they get it, though).

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This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review – Allan 25 mins ago

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