http://walletdvl5avrmoxk2fwsf5b76zkmbkoo3r6kqeesq5hsgnq7xhbciad.onion/non-blockchain-attacks-on-privacy
The solution is to encrypt addresses where appropriate or use another way of somehow hiding them from an adversary as per the threat model. Sometimes the eavesdropping can be very trivial, for example some forum users publish a bitcoin donation address on their website, forum signature, profile, twitter page, etc where it can be picked up by search engines.