By Matt Odell.

For many years there has been a common misconception that bitcoin is private by default. The reality is that many bitcoin users are extremely easy to track. Every transaction is recorded forever in the block chain; publicly visible to all participants. If personal information is linked to a specific transaction - name, email, IP address, mailing address, phone number, twitter account, etc. - that information can then be used to track past and future transactions using publicly available data. As bitcoin has matured, so have the tools used by surveillance companies. Bitcoiners should assume these companies have large datasets which combine information from many disparate sources including public on-chain metadata and private off-chain information used to improve their transaction tracking capabilities across the network as a whole.