Blockstream CEO Adam Back:
"Some of the exchanges and wallets are using tracing services, and [if there is a connection to illicit activity] up to four hops deep away from you, they will freeze your account."This threatens fungibility. Possible solutions are anonymity services like JoinMarket, Tumblebit and MimbleWimble
What If One Bitcoin Isn’t Like the Others? Fungibility Debated At Scaling Conference | CoinDesk
This guy is so full of shit. All they can see is the public key and nothing else. Anything like Alpha Bay change the keys every few days so u can't track anything. All they have is a hexadecimal key which doesn't link to anything. RSA encryption cannot be broken because no computer can hash the prime numbers p and q so even if you have a public key without the corresponding private key u can't trace ur BTC to any website. If you're seriously paranoid u can tumble ur coins.