For the past few minutes Google SERP pages have become completely unusable. Any result is flagged with the This site may harm your computer warning message, it doesn't matter which query you are searching for.
Here's a screenshot.
Funny enough, Google also flagged itself as potentially harmful.
I suppose the problem is caused by a really weird bug. Changing browser or logging out of your Google Account doesn't matter, thus I guess this bug should affect a very wide range of users.
UPDATE: A thread is available at the Google Blogoscoped forum, #googmayharm can be used to track the conversation on Twitter.