The Secret Star is a hidden joke on the original SPHDZ website, created by Michael K. Unfortunately, Michael has always been incompetent at hosting websites, and the joke does not work correctly; as a result, it has not been experienced by many people.
How the joke is supposed to work
On the SPHDZ website, there's a particular star in the background that you can click (it's shown in the picture to the right, but you may need to click the picture to zoom in and see where the cursor is pointing). When you do, you're told that you've found the Secret Star. What's supposed to appear next is another message telling you to click again, and this would go on for quite a while but would end eventually. Unfortunately, Michael has provided a private link that only he has access to, so you can't actually get past the first "Click Here" screen.
But never fear! You can still experience the joy of the Secret Star!
How to get the Secret Star to actually work
Once you click on the Secret Star and click again like it tells you to, you'll get a missing page error. However, the page is there, the link is just wrong. Go to the correct page and it will tell you to click again... but if you do that, you get another error, so don't. Instead, click Refresh. It will act as though you've clicked again. Keep doing that. You'll know when it's over.