Google Search is currently broken

Google Search appears to be broken worldwide.

At the time of writing - 15:10 on Jan 31st - Google Search is broken. All search results -- including Google itself -- are being flagged as "This site may harm your computer", and going through to the found sites requires a cut and paste from the Google warning page that follows. This is affecting at least www.google.com and www.google.co.uk, and has been like this for at least ten minutes.

I've also had direct reports from elsewhere in the UK that this is the case, and there are hundreds of Twitters from around the world saying the same thing.

UPDATE - As of 15:20, the problem now seems to be fixed, and Google's search reports are normal again.