As add-ons are programs downloaded from the internet, they are potentially malicious. You should only download add-ons you trust.
To download this add-on, please copy and paste the following code into Anki 2.1:
If you were linked to this page from the internet, please open Anki on your computer, go to the Tools menu and then Add-ons>Browse & Install to paste in the code.
All Anki 2.1.x Add-Ons
So it seems to be an add-on from the anki-developer