Our sites were briefly dropped from the organic listings today - about 2-3 hours at the most. But the panic that sets in definitely added some grey hairs and stole a year or two from my life expectancy.
It is interesting how the vagaries of your search listings can impact your world. One minute you are doing the regular day-to-day work, the next you are madly calling everyone who may be able to help.
Talk to the IT department to see if they had done anything.
Call your hosted security people to see if the firewall was changed or if they had adopted some type of redirect.
Talk to your media buyer and see if he has a new publisher that may be doing something wrong.
Check all your inbound links to see if they are changed in some way.
Go to the other major engines and see if you can see anything there.
You know that the loss of organic results if sustained will mean 100s of thousands of dollars in lost revenue...
Turns out Google was just doing some data center updates and some sites were dropped and then reset - according to Google.
Hey can't get rid of the new grey hairs but at least we are back in the warm embrace of Google organic!