Your website is blacklisted because Google scanned your site and found harmful behavior. Google needs to protect its users from dangerous websites that show up in their search results. In fact, websites that repeatedly get blacklisted for malicious behavior are limited to only one review every 30 days. That big red splash page (and warnings next to your site in Google's search results) are designed to stop visitors from entering your site. It works, too. Websites lose about 95% of their traffic when blacklisted by Google.
Our friends from Sucuri have discussed the steps on how to resolve this warning on your website. Visit their complete guide here: https://sucuri.net/guides/how-to-remove-google-blacklist-warning/
