# Using Blacklisting Tokens as Currency

Using a token that allows backlisting (e.g. USDC) as your [assertTruth](https://github.com/UMAprotocol/protocol/blob/dd9d1fa988d8520ad36db145db13591e9a104fa9/packages/core/contracts/optimistic-oracle-v3/implementation/OptimisticOracleV3.sol#L138) `currency` opens up a griefing vector that integrators should be aware of. 

The [assertTruth](https://github.com/UMAprotocol/protocol/blob/dd9d1fa988d8520ad36db145db13591e9a104fa9/packages/core/contracts/optimistic-oracle-v3/implementation/OptimisticOracleV3.sol#L138) and  [disputeAssertion](https://github.com/UMAprotocol/protocol/blob/dd9d1fa988d8520ad36db145db13591e9a104fa9/packages/core/contracts/optimistic-oracle-v3/implementation/OptimisticOracleV3.sol#L220) functions allow the caller to set any address as the `asserter`  and `disputer` that will receive payouts if their assertion/dispute is correct upon settlement. If a bad actor calls these functions and specifies a blacklisted address for repayment, the [settle](https://github.com/UMAprotocol/protocol/blob/dd9d1fa988d8520ad36db145db13591e9a104fa9/packages/core/contracts/optimistic-oracle-v2/implementation/OptimisticOracleV2.sol#L498) function will revert and cause the request to be frozen unless the address is unblacklisted. This costs malicious users their bonds and does not result in any gain, but freezing the assertion could cause issues for the integrator. 

Integrations that use tokens with blacklisting functionality should ensure that they have a way to manage frozen assertions (e.g. an admin function that can ignore a frozen assertion) without negatively affecting their integration.


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