Unfortunately (and here's the human error), the URL of '/' was mistakenly checked in as a value to the file and '/' expands to all URLs.
Wow, one character. That was one expensive character.
Wow, one character. That was one expensive character.
Six sigma, baby!
Seriously, though: We've all made similar mistakes before (though, after the first few times, we usually try to catch them on the dev server or the staging server). The trick for Google will be to ensure that this one is not made again.
I tell myself that all the time. And then I pause, and sigh, and load up the dev site anyway, just to make sure the home page has not exploded. Because sometimes it has. Typos happen. Brain farts happen.
Obviously I wouldn't necessarily expect Google to test a dev server by hand every time they change some code. That procedure is for little people like me. [1] For something as important as Google I'd expect there to be a procedure whereby each new change gets pushed to a small group of boxes, which then run a few really simple automated acceptance tests ("If I do a search for a random term, do I get back a page with links that can actually be followed?") before the thing gets pushed live fifteen minutes later.
Apparently I expect too much. Perhaps I'm overengineering this. Maybe it's okay if, a couple of times a decade, we just cripple half the Internet for 30 minutes and give 5% of the world's computer users a virus scare.
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[1] At least until I get lazier (in the Larry Wall sense of the word) and write some more scripts.