Random devices on my network displayed in Windows explorer under the network section

Me too!

I also have popping up from time to time a sitara  (mac addr a4 d5 78 17 b4 e1)  but also an " mstar-edison  (mobile phone?) macaddr 00 84 00 03 cb 6d. Mstar edison is not a phone brand or service provider I am familiar with in Australia by the way. I suspect it is a controller for smart lighting in a nearby apartment - I live in an apartment block in Sydney and I see them mostly after dark which currently means after say 6 pm since we are currently in mid-winter. .

 My passwords are in ancient greek, which cannot be all that common nowadays so I think it very very unlikely that it is a "hacker".   I am not using any mains electricity supported  pseudo ethernet connections (WD-livewire etc) anymore and most of my own  connections to the router are cat6 ethernet - ( Yes I paid a lot for that! Yes it was worth it., I think. ).  Everything else checks out normally with the proviso that in the evenings the lights on the router are indicating more traffic than I can account for because although I do have quite a lot of devices (smart tvs etc) connected, most of them are powered off.  (Yes I know they have to update firmware/program guides etc but I did the exercise of turning things off to isolate where the traffic was without success.  Would be nice if the router logged it conveniently eg by macaddr - for subsequent analysis. )

What I most want to know is how are these ghost devices connecting?  On the face of it they are getting in wirelessly but bypassing security! very worrying! Yet clearly they are, else it would not be possible to see their macaddrs.  I have seen them on win 7 and win 10 pcs. I check regularly and am a stickler for keeping antivirus etc up to date so we haven't had any of those problems for decades. 

My router is a 7000p about a year old. Very pleased with it apart from the floppy aerials which dont seem to have any facility for tightening up in the desired position. (?) And I would prefer the usb3 port on the back, not the front guys. Oh and (sorry about this) the overhang at the back means it is very awkward to reach ethernet ports etc if like me you have it high up for better clearance.

I do have a Google home mini, but no other associated smart devices. (Been doing a lot of the "smart home" stuff for years actually without it. )

I think this is potentially a very serious problem. If somebody is manufacturing things which can just "sneak in" whenever they want,  it needs to be sorted out asap before that "technology" finds  other uses. I am turning on Access Control and blocking the above macaddrs but one cant do that unless  you've id'd the macaddrs. Blocking all new devices seems a bit over the top to me.

Regards

Arthur T.