In their blog, Google posted this funny news

The Google Blog was unavailable for a short time tonight. We quickly learned from our initial investigation that there was no systemwide vulnerability for Blogger. We'll let you know more about what did happen once we finish looking into it.

And they updated it :
Update: We've determined the cause of tonight's outage. The blog was mistakenly deleted by us (d'oh!) which allowed the blog address to be temporarily claimed by another user. This was not a hack, and nobody guessed our password. Our bad.

Indeed ... their bad !