The counterparty protocol is built inside of the Bitcoin network. All assets (including FLDC) are built on this platform. It houses the assets inside of the Bitcoin network by using the 140 bytes of unused data in every BTC transaction. So everytime you send or receive FLDC, you will notice it shows up in the blockchain as a 0.00006 BTC transaction. This actually represents the Counterparty asset. http://blockscan.com/ is a site that decrypts this information and displays it as the assets, blockchain.info will only see it as a BTC transaction.

So this prevents the double spend, because Counterparty is secured by the BTC miners, so the hashing power of the BTC miners is the same as the Counterparty assets. Only an attack on the Bitcoin network would affect FLDC