It's very easy: my tool opens the profile site of every user. The same as you click on it with your browser. But the tool does this automatically for thousands of profiles. Each profile site will be "parsed" for the member status and the signing date (e.g. first chronological entry of "xxx has updated his profile") All these data will be summarized and voila - you have a full memberlist with member status (and mostly the signing date). From this list you can create the chart.
Here's a current screenshot of my tool (i don't want to publish the paying member numbers for now):
It's no cracking/hacking the database or anything illegal. If you had MUCH time, you could do it manually with your browser. Click on every user and note the member status. At the end, you will have the same numbers as mine.
I've done it primarely for me. And it seems, that most users here are not very interested in these numbers anyway.
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