DNSChanger is a piece of malware (i.e., virus) that's supposed to be infecting millions of computers at the moment. If you have it on your computer, it will stop connecting to the Internet on Monday.
To find out if your computer is infected, go to this page. It will probably give you, as it gave me, a clean bill o' health. But if it doesn't and/or you want to learn more, go to this page.
[NOTE: This is a revised post. I got the story wrong, then received a flood of messages telling me I got it wrong. It is now right.]