Checking for blacklisted IPs

I had a project where users were reporting intermittent flags from malware software. This wasn't something I had encountered before, but apparently if a scammer uses a hosting service's ip address, they get put on various blacklists, and then an innocent project can then accidentally inherit this blacklisted IP causing problems. The solution is to check the IP for problems and complain if there are issues. There are some sites that allow you to check for this for free here:

The sites will also scan for other potential issues which may be missed such as DNS configuration errors, as well as malware itself.