If you are a proud owner of a D-link your best bet today is to hide in a dark place in shame. At least if you trusted D-Link to make a solid and secure product that is also cheap to purchase. Reading the link it is pretty obvious that D-link wanted to provide a simple auto update functionality for its customers but sadly failed miserably. With the external management interface enabled you have let your D-Link totally open for external control due to Joels backdoor.
So, in order to create a low-cost product, D-Link obviously has cut down on security testing. This sadly goes for most within IT. If it is cheap chances are that there are a number of security vulnerabilities and bugs.