How to create/delete a HomeGroup in Windows 8?

How to create/delete a HomeGroup in Windows 8? I never used homegroups. Now, when I enter HomeGroup control panel page, I see that somebody has created homegroup on the network. User name and computer name displayed. I don't know who is this. I don't know such a computer. I am at home and I know all computers here. No one has this name. How to create my own homegroup? How to delete this parasitic homegroup? Windows manual says that everybody should leave a group then it will disappear. In my case there is no one in the group (mystic person only). How to delete a group? UPDATE Also I can't join this group. System asks a password from me. But I don't know it. And I can't ask it from that person because he does not exist. UPDATE 2 I have no Create a homegroup button. It is replaced with Join Now button, since group is treated as existing. UPDATE 3 This is probably notebook I was taking from my friend long time ago. Notebook is already gone and no access to it. Most probably it was connected to my home WiFi. Probably I clickded "create home group" on that notebook. So what? It infected my network forever? SOLVED My fault. This was a computer from VPN I participating. Anyway it is strange that computer can participate multiple LANs while homegroup can be only one.