Is the domain name banned in any of the internet search engine results such as Google or Bing? If the domain name was used for a website and it hosted spam content or the website owner violated search engine guidelines, the domain name could be banned in the search engine, and removed.
If the website is a live website on the domain name, and it's currently banned in the search engine (it's not found in the search results pages), then that can indicate larger problems that the domain name has or could have in the future. If the domain name is banned in the search results and is a completely new domain name, not registered yet, or has expired (not renewed), it may be banned in the search engine results. In those cases it can get listed again and may not have any future problems.
In any case, a domain name that is banned in the search engines typically is not a good thing. DNProtect believes that domain names that are banned in the search engine results can indicate other potential issues, so will assign negative points for domains banned in search engines.