I'm guessing IHBT, but here's an explanation for those who don't quite get it:

He typed: at midnight `shutdown -r now`
He meant to type: at midnight "shutdown -r now"
The "at" command schedules the command in quotes to run at midnight. Putting backquotes around the command, as he actually typed, causes the command to be run immediately.

Unless he meant that there are only about thirteen hundred of them out there. It sure would explain why people ask me to fix their computers so darn often.