The first step in securing a newly deployed server is toclose unnecessary service ports. Open ports can expose the server to unauthorized access and potential cyber threats. By closing unused ports, the attack surface is reduced, limiting the number of entry points available to attackers.

Updating the software version (B)andupgrading the OS version (D)are important security measures but should follow the step of securing open ports to prevent immediate exposure to threats.

Adding the device to the Access Control List (ACL) (C)is a step in network security but does not directly secure the server itself against potential attacks.

Closing unnecessary ports helps in minimizing the risk of network-based attacks, such asport scanning and exploitation of default services.