(Maybe someone here will know ...)

My computer is repeatedly adding PublicWifi and xfinitiwifi to the "preferred networks" list, without my knowledge or consent. I have tried various options but the problem persists. I remove them, and they will reappear. (I never "joined" these networks.)

Although there is a xfinitiwifi open wireless within reach of here, there is no PublicWifi on the air.

Ideas? (OS/X El Capitan ...)

I can tell that there must be a (privileged!) "rogue" at work, because an entry appeared in the list overnight . . .

Maybe that's an OS/X "feature". I've never used any Apple product, so I have no other suggestions. I'm blissfully ignorant.

Actually, I so-far think that I have traced it to the login of a particular (again, non-privileged) user. Perhaps OS/X keeps a per-user "preferred list," silently updating the master from it. We shall see . . .

I recently discovered that for several users, these entries had been added to:

~/Library/SyncedPreferences/com.apple.wifi.WifiAgent.plist

... on several user accounts.

I can say for certain that none of those users, nor I, ever consciously added these networks to any list anywhere, never knew about these networks and have never subscribed to them. But, this could be the mechanism ... or part of it ... by which these SSIDs continue to appear in the "trusted" list.

=====

I am going to mark this thread as "solved" because I believe that this is the mechanism ... and I am going to raise it as a security issue with Apple because I believe that it trusts a PList ... which is not a protected file. A mechanism should exist to strictly control (i.e. require admin password) what SSIDs are in the connection list, and this appears to be a way to circumvent it. Comments welcomed.