Instructions
To analyze your smart contract for potential vulnerabilities, paste the hexadecimal bytecode of your compiled smart contract into the textarea. This bytecode is generated during the compilation process of your smart contract source code.

You can use truffle to compile and generate the bytecode of the smart contract. The bytecode is an entry named bytecode or deployedBytecode in the generated json (i.e. MyContract.json).

truffle compile MyContract.sol

What is smart contract bytecode?
Smart contract bytecode is the low-level, machine-readable representation of your smart contract. It contains the instructions that will be executed on the blockchain. Our tool uses this bytecode to identify potential vulnerabilities and security risks.

About privacy
There is no data that we keep. The bytecode that you are going to paste into the textarea is completely non-sensitive and public. The Ethereum blockchain powers it, and it's always available. As such, there is no need for you to be concerned about any privacy-related concerns with your smart contract.