First they were worried about Bitcoin, and now Monero. What's next? Z-Cash?
They should understand the fact that there are probably more than a thousand cryptos out there, many of them are privacy-focused. How many of them can be kept under their watch? They can't do shit. Game over.
Actually they can do a lot, they can easily install spyware on target computers without the users ever knowing about it.
The FBI has a wide array of "investigative techniques" ...