The Securly SSL certificate is essential to filter HTTPS sites correctly. To install the certificate on your Windows Server:

1. Open Administrative Tools, and then click on "Group Policy Management".
2. In the console tree, under the top level of the domain, right-click and create a new policy named ‘Securly SSL’. 
3. Double-click on Group Policy Objects in the domain containing the Securly SSL Group Policy object (GPO) that you want to edit.
4. In the Group Policy Management Console (GPMC) navigate to Computer Configuration > Windows Settings > Security Settings > Public Key Policies. 
5. Right-click the Trusted Root Certification Authority store.
6. Click on "Import" and follow the steps in the Certificate Import Wizard to import the certificate. The Securly SSL certificate is attached at the end of this article.