If you buy bitcoin from Coinbase or one of the bitcoin exchanges those bitcoin could possibly be traced back to you because you had to provide personal information to open the account.

If you then need to send those bitcoin anonymously you can use a mixing service that substitutes coins that belong to someone else for yours. The most popular mixing service was Instawallet, which was taken down by hackers and is no longer in operation. Another, more secure online wallet now provides a mixing service.

‘Send shared’ is a mixing service provided by blockchain.info. You do not need to have a MyWallet account to use the mixing service. Just use Tor to visit https://blockchain.info/wallet/send-shared and enter the bitcoin address you want to send payment to anonymously and click ‘create forwarding address’. A window will open with a forwarding address to send bitcoin to that is valid for 8 hours.

You can send bitcoin to the forwarding address and blockchain.info will then substitute someone else’s bitcoin for yours and send to the destination address. Blockchain.info also provides a ‘taint analysis’ tool that you can use to verify that the bitcoin were properly mixed. There is a very reasonable 0.5% fee to use the mixing service, the mimimum quantity you can mix is 0.2 bitcoin with a maximum of 250 bitcoin. Always connect to blockchain.info using Tor or an anonymizing service like Private Internet Access, and if you choose to create a wallet at blockchain.info never verify your account or provide an email address or phone number.

Consider using blockchain.info’s send shared whenever you buy new bitcoin: transfer the coin from your broker to your wallet using send shared as the intermediary. It is important to use a separate wallet for your anonymous bitcoins, and do not transfer bitcoin from addresses that can be traced to you into your anonymous wallet or you will taint the wallet. You can correct by sending the bitcoin in that wallet through the mixing service again.

Other mixing services are available, see https://en.bitcoin.it/wiki/Category:Mixing_Services for a current list. Only blockchain.info provides a tool that you can use to verify anonymity.

Using a mixing service to anonymize your bitcoin does require you to trust that the mixing service does not keep logs. If you do not want to use a mixing service and need anonymous bitcoin you can buy bitcoin with cash locally using BitInstant ( https://www.bitinstant.com/) or LocalBitcoins ( https://localbitcoins.com/).