The volume of suspected ransomware payments flagged by US banks has surged this year, on pace to nearly double last year’s, the US Treasury Department said, highlighting the scale of a problem that governments across the world have described as a critical national security threat.

Nearly $600 million in transactions were linked to possible ransomware payments in so-called Suspicious Activity Reports financial services firms filed to the US government in the first six months of this year. That is over 40% more than the total for all of 2020.