Windows 10: Phones appearing in Network

Solution 1:

I've found this thread on Microsoft forums. This issue is related to Windows Connect Now.

Solution: I disabled WPS (also called WCN in Windows) on the router.

In the forum, someone solved this by disabling the Windows service "Windows Connect Now". If you have many PCs on the network that solution is not the best. So, modifying the router setting for WPS stops this for all PCs.

Solution 2:

Non Paranoid Answer (more likely):

I'd recommending not broadcasting your SSID, not broadcasting shouldn't really hurt anything. The phones might be automatically trying to connect to your network because they see it, however without the password they should not be able to connect.

Paranoid Answer (less likely):

Granted wifi is known for its insecurity, so nothing would really stop someone from utilizing the phone's cell phone carrier to break your wifi via rainbow tables. For example, test your network, share the information to a server online that has rainbow tables and higher computation power and eventually figure out your password. Don't see why this couldn't be automated via an app... good thing I'm a white hat...