LAN computer of different Workgroup has Share rights

Hi,

I have a Win7 machine set up with a custom-named Workgroup. I then gave an XP machine I'm working on access to the LAN (via wireless router), and it automatically had access to my shared folder, even though its Workgroup name is different.

I had the XP machine on the LAN before, and I believe I was running it under my custom Workgroup, but when I gave it back to its owner I renamed its workgroup back to MSHOME, which it still is.

So I'm wondering where it is that I'm allowing anyone with LAN access to get into my shared folders. This should be regulated by Workgroup rather than by LAN, but I've got a leak somewhere.

Thanks,
p.

I see that the problem was that "Everyone" had viewing rights under my shared folder's Security settings. What I don't understand is

1. why the XP machine saw that folder under my Workgroup name yesterday, but this morning it listed the folder directly, without listing any workgroup name at all, even its own, and
   
2. whether it's possible to extend shares by Workgroup.

Thanks.