A security researcher named Dan Kaminsky released a fundamental flaw in the design of the internet today that allows hackers to, among other things, send you their own web pages when you request a url such as "google.com". The flaw lies in the DNS system that translates domains to IP addresses (numbers that identify your computer on the internet). When you make a request for google.com or any other domain name, you ask your ISP what the IP address for that domain is, and then you connect to that IP address. Kaminsky published a way for an attacker to flood any ISP implementing the DNS protocol with requests in a way that sends other users to any IP address the attacker wishes.

Here is his webpage. He also has a tool that allows you to check whether your ISP has patched their system yet.