If you did a search on Google between 6:30 a.m. PST and 7:25 a.m. PST on Jan 31st morning, you likely saw a message "This site may harm your computer" accompanied each search result. Google flags search results with the message, if the site is suspected malicious. The issue happened due to a human error that caused the “URL of '/' was mistakenly checked in as a value to the file and '/' expands to all URLs”, the Google team quickly reverted the file, reports Marissa Mayer.
In a related news, Gmail team has also posted about the implementation issue of Google's malware filters, used by Gmail's spam engine to help protect users from malware. The filter has mistakenly sent some legitimate mail to people's spam folders, between 6:00 a.m. PST and 8:00 a.m. PST. Google is working to roll out an automated fix, in the meantime, your requested to check your spam folder.
More info: StopBadware