The Reserve Bank of India said on Tuesday it had alerted banks of possible misuse of the SWIFT system on at least three occasions since August 2016. However, the implementation of its proposed measures by banks was “at varying levels”, the central bank said, without naming any bank.

The SWIFT infrastructure – Society for Worldwide Interbank Financial Telecommunications – is a messaging system banks use worldwide to send encrypted information and instructions. It was used to enable the transfer of funds in the Rs 11,380-crore fraud at the Punjab National Bank.

The RBI said it issues necessary instructions to banks from time to time on such issues and risks, including the risks due to “the potential malicious use of the SWIFT infrastructure”. The central bank “confidentially cautioned and alerted banks of such possible misuse, at least on three occasions since August 2016”, and advised them to implement safeguards, a statement said.

The central bank also said it had reiterated these confidential instructions on Tuesday and “mandated the banks to implement, within the stipulated deadlines, the prescribed measures”.

Though the statement did not describe any of the three instances, one such incident of abuse of the SWIFT system possibly involved Union Bank of India, The Indian Express had reported on Tuesday. The situation was purportedly “salvaged post event without any apparent monetary loss”, then Deputy Governor of RBI, SS Mundra had said in January 2017.