We added an advanced feature to prevent your transactions on being replayed on other chains, like ethereum classic. This allows you either to prevent that transfer on happening on classic at all, or use that transaction to send the same amount to a different contract, like a newly created account or an exchange. If you want to fully separate all your transactions we recommend you create two new accounts, one for Ethereum proper and the other for Classic, and then move all your funds into them (remember that you need ether to move tokens), making sure that each account has 0 ether on the other chain - doing this once would prevent any future transaction from being replayed. To use this, use the "more options" button on the send page.