If you want to get rid of any linkage, it's pretty easy. You can deposit coins in an exchange, then withdraw a few days later. That isn't a guarantee, but it vastly increases the probability that you don't receive any of your "old" coins.
Can you go into a little more detail about this? Perhaps specifically with how this would work with Coinbase? I was under the assumption that any bitcoins I deposited into Coinbase went into a wallet that belonged to me. So sending them all to Coinbase and then withdrawing them a few days later would just link everything to one address, and then everything from that address would come out into my new wallet, still linked.
Or do you mean sell them all off for fiat currency and then re-buy them all a few days later? Or something else entirely?
Let's do an example.
Say I buy something from you -- a pair of nuclear powered anti-fart underwear -- but the cops are coming down on people for that. You want to "clean" your bitcoins, so you:
- Deposit BTC in Cryptsy
- Buy LTC from Cryptsy
- Pull out LTC to a new LTC wallet on your computer
- Transfer LTC to BTC-e (then delete or abandon that LTC wallet)
- Sell LTC for BTC on BTC-e
- Transfer BTC from BTC-e to your "clean" wallet
Rinse and repeat as you like across different exchanges. The more you do, the "cleaner" it gets.
In more linear terms:
Deposit > Buy crypto > Crypto wallet > Deposit > Sell crypto for crypto (BTC or other) > Clean wallet
BTC > LTC > DOGE > XYZshitcoin > BTC
All done in different places.
You can sell for different cryptocurrencies at different exchanges. If you're using Bter, BTCChina and others, the trail will get very cold very quickly. Tracing anything would require the full cooperation of all the exchanges, which isn't likely to happen.
You can even transfer between different accounts on 1 exchange, making it all the more difficult.
You never touch fiat currency at all. Fiat has stronger AML and KYC regulation on it, which makes it harder to do with your own money what you want to do.
And you can always buy/sell through Localbitcoins, which will only make things harder if anyone wants to track anything.
That's just 1 way.
There are "mixers" that will mix coins for a fee. The end result is that it's impossible to tell where the coins came from.
For Coinbase, just pull them out and do the above, then send coins back.
However, what I've described above takes some effort, and really isn't necessary unless you're doing some really, very seriously shady stuff. Or anything seriously illegal, like contract killing.
You can completely screw up any kind of "tracking" by doing 1 simple step from above and depositing into a new wallet. If anyone is tracking you, like an ad company, or marketing company, you've just screwed them by creating an entirely new wallet that isn't linked to you. They could try to do pattern matching, but honestly... that's grasping at straws and they're unlikely to ever be able to do that, ever.
(I am missing some highly technical points above, but I've been conservative. For more information you can look into how wallets treat "change". Also look into "dust". It's probably not worth your time.)