Application Focus mysteriously disappearing

[Joachim]

When I am connected to the internet (via Modem) - and only then - there
seems to be a process that takes the focus away from any window that has the
current focus. Then I click back into my current window. But after a few
minutes the focus goes away again. I have checked the appropriate box in the
Tweak UI for Windows XP - box but without success. My virus checker hasn't
found anything - so I don't think it is a virus.

Thanks

Joachim