Before it was hrd to track the flow of cryptocurrency. Byt now it was in different manner. By using the Etherscn.io we can almost track the flow of crytocurrency. May be we can't find the address link to which person. But if you know the address of particular person, we can easily find the incoming transaction to the address .
It was not hard before to track cryptocurrencies transactions because the transactions are recorded on blockchain which can be tracked or traced. Blockchain was originally created by Satoshi Nakamoto in order to be able to track bitcoin transactions. There are very few cryptocurrencies that can not be tracked, like monero, but they are very few.