  Airdrops are a popular method of distributing cryptocurrencies and tokens.
While often considered risk-free from the point of view of recipients, their
impact on privacy is easily overlooked. We examine the Clam airdrop of 2014, a
forerunner to many of today's airdrops, that distributed a new cryptocurrency
to every address with a non-dust balance on the Bitcoin, Litecoin and Dogecoin
blockchains. Specifically, we use address clustering to try to construct the
one-to-many mappings from entities to addresses on the blockchains,
individually and in combination. We show that the sharing of addresses between
the blockchains is a privacy risk. We identify instances where an entity has
disclosed information about their address ownership on the Bitcoin, Litecoin
and Dogecoin blockchains, exclusively via their activity on the Clam
blockchain.
