http://bgr.com/2015/07/31/windows-10-upgrade-spying-how-to-opt-out/

Ive taken most of the steps in this advice, im not a guru, but for example my daughter uses a Surface Pro from my wireless modem router and then she goes to school gets on their network, so by theory she shares my routers connection info with all the school !. Not sure if this is true but from this article it is. Ive just renamed my SSID anyway.

It is technically true, but what it means is that it would share the SSID and connection info with people in her address book. Then, when they visit your house, they can connect their Windows 10 devices to you Wi-Fi automatically.

It does not tell everyone in the world what your SSID details are though...

SO then, because im a tight arse crusty old techology ( specifically Microsoft) hater i want to stop my daughters friends in her address book from instantly sharing my wifi details when they come round so i add the "_optout." to the end of my SSID. This will stop them from stealing my bandwidth and downloads ?

Pretty much, there are also the privacy settings within Windows 10 where you can turn this feature off too

Thanks mate.