"Hijacking DNS queries, sniffing and modifying HTTP in any way,
sniffing or modifying any kind of email or email failure,
redirecting IPs, transparently proxying web traffic, analyzing your
traffic, shaping your torrent-like or other rule matched traffic,
etc, etc -- you get the idea, are some of the more popular
techniques out there. In worst cases an ISP would even firewall
your inbound and outbound port access."