From CNN.com:
Worm strikes down Windows 2000 systems
A computer worm shut down computer systems running the Windows 2000 operating system across the United States on Tuesday, hitting computers at CNN, ABC and The New York Times.
Around 5 p.m. computers began crashing at CNN facilities in New York and Atlanta. ABC said its problems began [...]

There is a
new and improved MyDoom worm making the rounds on the Internet. It’s spread via a link in email. Clicking the link exploits a recently discovered buffer overflow in Internet Explorer. McAfee has a
more detailed description. Yet another good reason to switch to Firefox!