The group, which met on Monday, “included private sector members for the first time” who were invited “based on their specific insights to this incident,” she said.

Hacking groups are using recently discovered flaws in the Exchange mail server software to break into targets around the world.

The White House group noted that paying to mitigate the hack “weighs particularly heavily on small businesses,” Psaki said.

The breadth of the exploitation has led to urgent warnings by authorities in the United States and Europe about the weaknesses found in Exchange.

The White House group “discussed the remaining number of unpatched systems, malicious exploitation, and ways to partner together on incident response, including the methodology partners could use for tracking the incident, going forward,” Psaki said.

The security holes in the widely used mail and calendaring software leave the door open to industrial-scale cyber espionage, allowing malicious actors to steal emails virtually at will from vulnerable servers or to move elsewhere in the network. Tens of thousands of organizations have already been compromised, Reuters reported, and new victims are being made public daily.