The best immediate actions to prevent unauthorized server access are to stop all unneeded services and block the ports on the firewall. Stopping unneeded services reduces the attack surface of the server by eliminating potential entry points for attackers. For example, if the server is not functioning as a web server, there is no need to run a web service on port 80. Blocking ports on the firewall prevents unauthorized network traffic from reaching the server. For example, if port 80 is not needed for any legitimate purpose, it can be blocked on the firewall to deny any connection attempts on that port.