My bet, it's spam, they are totally trying to extorque bitcoin. It look like an automated message.
And from what we can read from there on Internet, they are sending this message to owners of google blogs ? and we know that for hacking a google blog, they require your google account, which I doubt it was hacked.
Anyway, you can look at your file structure, DNS records, etc to see if something is weird but in every case, DO NOT PAY ??
I am quite confident to say that your are still safe ? make your best poker face ?