In this regard you might also mention 21.co (now bitnodes.earn.com) and their constant monitoring of Bitcoin nodes. The node addresses are made public for all the world to see. And they could be monitoring transactions too but not making this info public.
In this regard you might also mention 21.co (now bitnodes.earn.com) and their constant monitoring of Bitcoin nodes. The node addresses are made public for all the world to see. And they could be monitoring transactions too but not making this info public.