Google says it will be rolling out the new system slowly. The new warning system is designed to include pages that may not be malicious but indicate that the site might not be completely under the control of the legitimate site owner. The Anti-Phishing Working Group estimates that between 75 and 80 percent of phishing sites are legitimate sites that have been hacked and seeded with phishing kits designed to mimic established e-commerce and banking sites. Google promises to increase the number of pages flagged as potentially compromised by hackers.
Source: https://thehackernews.com/2010/12/google-debuts-this-site-may-be.html