What is an 'Open Microsoft SQL Server'?
Your server operates a Microsoft SQL Server Browser service responding on port 1434. When this feature is enabled and publicly accessible from the internet, attackers may use this service to launch denial of service attacks (an amplification attack using forged UDP packets).
Reconfigure your server in such a way that this service can’t be exploited anymore.
This can be achieved by blocking access to port 1434 or disable the SQL Server Browser service entirely, which shouldn’t have any impact if you run only one instance of SQL Server.
If you need access from remote machines to your Microsoft SQL server, then configure your firewall to only allow connections from trusted sources.
You can check if the port is still open by using a tool called 'nmap' and by running the following command:
$ sudo nmap -sU -pU:1434 -sV IP_address_here_