How to create/delete a HomeGroup in Windows 8?

Question

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.

Answer 1

Homegroups are kept up only while at least one machine is still active in the group. Some Windows 7/8 machine in your network is still a member of that homegroup.

The only way to remove a homegroup is to log on the PC that is a member and remove them from that group. The password for the homegroup will be stored on a member PC should you want to access it.

If you are running a router with an open WiFi it's possible that a neighbor could be on your network and you are detecting them. You can check who is on your WiFi by checking the DHCP lease table on your router.

Creating a homegroup is extremely easy. Follow this tutorial. As per Microsoft:

To create a homegroup

1. Open HomeGroup by clicking the Start button , clicking Control Panel, typing 
homegroup in the search box, and then clicking HomeGroup.

2. On the Share with other home computers running Windows 7 page, click Create 
a homegroup, and then follow the instructions.

Answer 2

Had the same problem. I was about to try the suggested solution posted here (which looks promising) when I stumbled on an easier solution.

Go to: Control Panel -> Network and Sharing Center. Look at the link next to the "HomeGroup:" field (upper-right of window). When I did this, it said "Create" and allowed me to create a new one. (After doing so, I also changed the password to one I could remember so I wouldn't run into this problem again.)