Depends on the jurisdiction. For instance Europe allows reverse engineering for inter compatibility. Terms of services carry little value here (none for this cl

Depends on the jurisdiction. For instance Europe allows reverse engineering for inter compatibility. Terms of services carry little value here (none for this clause that's already covered by a specific law). However, it would be interesting in the case of bank services. Accessing the account from the customer probably let you initiate a variety of actions like money transfers or loans, it's sensible to argue for limited and controlled inter interoperability. Also, customers are not allowed to share their credentials and he is in breach of his contract. The account should be considered compromised and be locked.