Quttera's support team is being constantly contacted by website anti-malware monitoring
customers whose website(s) were blacklisted. This post lists several (not all) blacklisting authorities and how to submit your site for (re)testing by them.
First, you should make sure your website no longer hosts malware, spam or any other potentially harmful content. You can do it by yourself or if you're ThreatSign customer you can simply let us do it for you.
To check by yourself, you can start with online scanning via VirusTotal and/or Quttera online scanner. When reviewing the reports make a list of vendors that detect your website.
For example in VirusTotal report: