The biggest bank in the Nordic region says this month’s ransomware attack underscores the need for lawmakers to look more closely at bitcoin’s role in financial crime.

Nordea Bank AB, whose chief risk officer, Julie Galbo, testified to the Danish parliament in response to questions about management’s efforts to fight money laundering, says virtual currencies like bitcoin are making that battle harder to win.

“Bitcoin is an unregulated and opaque currency that’s often used in shady transactions,” Galbo said. She says bitcoin represents a “big risk” standing in the way of efforts to fight money laundering because of the anonymity it affords those who use it.