1) Disable WAN administration to prevent outsiders from gaining control of your LAN:
Connect to the Cayman as 'admin'. Select Configure, then WAN, then "your connection type" (in the "WAN IP Interfaces" box). Then, in the Restrictions control, select "Admin Disabled". Then, you should get a yellow warning icon in the top right of your browser window. Click it, then click the thing that comes up to save your changed settings and restart the Cayman.
2) If WAN administration is not to be disabled, change the name of the SNMP community from the default of 'Public', again to prevent outsiders from gaining control of your LAN:
Connect as 'admin', select Configure, then Advanced, then SNMP (in the Services box). In 'Communities', type a name that only you will know. Just about anything, e.g., 'housebat' or some such nonsense. Click the Add button. Then, select the 'Public' entry and click the Delete button. Save the settings and restart the Cayman.
3) Enable a non-existent default server to trap any unwanted outside server requests:
Connect as 'admin', select Configure, then Advanced, then Default Server (in the NAT box). Check the 'Enable Default Server' box and enter an IP address in the 'NAT Server IP Address' box. The IP should be within your DHCP range, but one that would never be assigned to an actual computer, e.g., 192.168.1.253. Click the Submit button. Save the settings and restart the Cayman.