Check if your website is identified as having malware or exhibiting phishing activity by Google's safe browsing API. Any site containing malware or suspicious for phising activity is seen as a threat to the online community and is often penalized by search engines. This test checks your website against regularly updated malware and phishing databases of problem websites.
Check your URL:
How do I fix it ?
If your site is reported as unsafe (with malware or phishing activity) you are advised to contact your host, identify the problem, quarantine and clean your site.
Here you can find a complete guide for what you have to do in this case.