Fresh install (WinXP SP1 patched to SP2), and then Avast Home! (Free).
I've been using it for a long time now (two years to say the least) and I really like it.
This never happened before, maybe a newer release is doing so.
It's most likely to happen when I leave uTorrent, Firefox & aMSN open for long periods of time (days, a week, etc.).
The port use is normal right now. Sorry, when this issue happens to me again, I'll post more info and screen captures.
I was just reporting it, maybe someone else is having the same problems.
EDIT: Maybe it has something to do with UPNP or Windows Firewall?
Regards
-Martín