BRUSSELS (AP) — International money transfer supervisor Swift has warned that a new cyberattack has been made against a bank, which it did not name, and has urged its clients to urgently review their security systems.

Belgium-based Swift said in a statement Friday that attackers had used malware to target a PDF reader at the bank, allowing them to transfer money and tamper with bank documents.

It did not say whether any money was taken.

Swift said forensic experts believe the use of the malware is "not a single occurrence, but part of a wider and highly adaptive campaign targeting banks."

It underlined that the Swift system had not been compromised by the malware.

Swift said "the attackers clearly exhibit a deep and sophisticated knowledge of specific operational controls within the targeted banks."