Strange Network in My Network Place

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