http://walletdvl5avrmoxk2fwsf5b76zkmbkoo3r6kqeesq5hsgnq7xhbciad.onion/blockchain-attacks-on-privacy
This is what leads to bitcoin's unique value proposition as a form of electronic cash which requires only small amounts of trust. But the same blockchain structure leads to privacy problems because every transaction must be available for all to see, forever.