I'm seeing lots of reports from friends, colleagues and Twitter postings about oddities at Google, which I've reproduced below. Every single result that's being returned as a 'This site may harm your computer.' warning. Clicking on the warning itself just results in a 502 Server Error message. Interesting - I've not seen this before.
Clicking on the appropriate page link leads to Google intercepting the query and displaying their warning page - so you have the bizarre situation of Google warning searchers against visiting.. Google!
There are huge numbers of comments already on Twitter... coming in at the rate of about one every 2 seconds at the moment.
UPDATE!! SIGNING OUT OF YOUR GOOGLE ACCOUNT REMOVES THE ERROR MESSAGE.
Another update - everything now seems to have returned to normal. Everyone can go on about their business, nothing to see here. Move along now!