Design a banking system to facilitate account creation, deposits, transfers, and listing the most active accounts by total monetary activity, with commands entered via parsing CSV/JSON.

Focus on outlining the architecture of the banking system, emphasizing how each component interacts with one another. Start by detailing the data models for accounts and transactions, ensuring you cover the necessary attributes for each. Discuss how you would implement the CSV/JSON parsing logic to handle user commands, including error handling and validation. Consider scalability and performance when listing the most active accounts; think about how you would efficiently aggregate and sort transaction data. Finally, touch on security measures for protecting sensitive user information throughout the process.