Disabling Telnet on servers and network devices is correct because Telnet is an unencrypted communication protocol that could expose sensitive data to interception. Instead, more secure alternatives like SSH should be used. Changing the default VLAN mainly protects against VLAN hopping attacks and does not disable a network service. Configuring the firewall to block ports unrelated to services offered by the network does not disable a network service but controls access. Using strong encryption for remote access is a security measure but does not involve disabling any services.