Optus portscan. If they find port 80 open, they'll cut you off.
What IP address do they use for the portscan, a simple firewall rule could fix that :-) They also scan for mail server ports.
I was told over the phone that there were no restrictions to running a server on my system, the web paints a slightly different picture however. Don't you love the guys on the end of a sales phone that have absolutely no idea.