Strange Network in My Network Place

[Jonathan]

Hello All.

My domain is a windows domain with windows 2000 and 2003 server. The
computer on the network are windows 2000 and XP.

Tonight I'm doing maintenance on the network and see something that is very
weird.

My domain name is: mydomain.com but when I open My Network Place\Microsoft
Windows Network, I see a lot of domain there, not only mydomain.com.

I can see a list of domain like domain1, domain2, domain3, asf ..... like if
these domain are linked to our network. All the domain that I see in this
list are concurent company and I'm pretty sure that someone in our company
visit their web site during the day.

Why I see many domain in "My Network Place\Microsoft Windows Network" that
are not part of my network ?

Is it a security hole on my network ?

I'm scare a little bit.

Thanks.

Jonathan