Major U.S. banks are pushing the Swift messaging network to boost security following cyberattacks in Bangladesh and Vietnam involving fraudulent transfer requests, Bloomberg News reported on Tuesday, citing people familiar with the matter.

Some U.S. banks want to discuss with Swift whether it responded quickly enough to the breaches and if it should help banks better secure their systems, Bloomberg cited one unidentified source as saying.

Some U.S. banks expect Swift to come up with a technological solution to reduce the risk of further attacks, the report cited a second unidentified source as saying.

Swift codes for at least seven international banks were written into malware used in an attack that Vietnam’s Tien Phong Bank disclosed over the weekend, Bloomberg reported, citing a private report published by BAE Systems PLC.

The malware was configured to hide transaction messages involving those banks, Bloomberg reported. It said they included Industrial & Commercial Bank of China Ltd., Bank of Tokyo-Mitsubishi UFJ Ltd., UniCredit SpA, Australia & New Zealand Banking Group Ltd., United Overseas Bank Ltd. of Singapore, South Korea’s Kookmin Bank and Japan’s Mizuho Bank Ltd.

The revelations that such banks were mentioned in the code raised concerns of global lenders because they show that the attackers were not focusing solely on small banks in developing nations, Bloomberg reported, citing people familiar with several banks in the U.S. and Europe.