On OS X when I plug in a new USB based Ethernet device, the first thing it does is pop up a dialog asking me if I want to enable/configure the device... is the device already configured at that time?
I run as a non-administrator account, so this may be different if the user has administrator privileges.
But here is what happens:
1. I plug in the new device
2. Dialog box pops up letting me know a new network interface was detected (and to open network preferences to configure the device). The device does show up as en6, it is disabled and there is no network activity.
3. I can click Cancel or open Network Preferences
4. Click to open Network Preferences
5. I have to click the lock, and authenticate as an administrative user
6. I have to click the +
7. I have to select the new network interface by name from the drop-down
8. I have to click OK
9. I have to click Apply
At that point the network interface is brought "up", and it does a DHCP request, and I can use it.
So there are 8 steps to take AFTER plugging in the device before it can start siphoning off any and all of my data. It's not as plug and go as it is made out to be.
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After adding a device, you can remove it from the list of devices in Network Preferences, and that resets that dialog box letting you know there is a new device.