The "even" in your subject seems misplaced. It would be remarkable if it came up while you were connected.
A previous discussion on the same problem, leading to a very happy end in the Security Forum later on, is http://reviews.cnet.com/5208-6618-0.html?forumID=6&threadID=13252&start=0
The link in the Security forum: http://reviews.cnet.com/5208-6132-0.html?forumID=32&threadID=13347&start=0
You would be very lucky if this was the exact cause with you. It could very well be another program, leading to another solution. Start searching then, and let's hope you're as good a researcher as Dorothy. And that it isn't some nasty spyware with you.
This really can't be done from a distance, as you'll understand.
Good luck, and keep us informed.
every few minutes the window pops up as if i had opened windows explorer to go onto the internet and wants my user name and password to log me on. i keep clicking cancel but it keeps appearing every two or three minutes and is most annoying, especially when i am working off the net to start with. Help!