Installation is detected if.

• User comes from referer site
• I check do i have this referer in my database if i do not have it
• I download referer page and check for live helper chat code.
• And ony then I increase counter, so you can imagine that downloads number is much bigger :)

I do not have any secret code in installation process itself wich would inform me about installation so installation number is much bigger i ques. :)