Authorities arrested seven people allegedly involved in the operation and seized 1,200 SIM boxes containing 40,000 active SIM cards.

SentinelOne and Beazley Security say the group has been evolving its techniques of late, all with the goal of making money off stolen data.

The 21 signatories support a number of steps, such as banning vendors who behave illegally, in a document agreed to last week in Paris.

CISA's director said that the vulnerability "is one of the most serious I've seen in my entire career, if not the most serious."

The $2 billion Austrian firm said on its website that an "ongoing" incident was affecting its ability to process orders.

The attacks were anything but unique. Still, they worked.