Since over $70 million in Bitcoin was stolen yesterday by an attack that exploited a fault in the Coldcard’s system, it has been reported that the thief used a top blockchain services provider for help. 

Writing on X Friday, engineer at payments company Block, Clay Garrett, said that the provider — who he did not name at the request of the services provider — had been contacted after finding blockchain movements matched the “suspected workflow” of the attacker. 

“During our investigation of the Coldcard drain yesterday, we identified an unusual pattern in the sweeps,” Garrett said. 

“That pattern led us to a hypothesis that has since been confirmed: the operator used a paid account at a well-known blockchain-services provider to query the source addresses and perform other related activity during the sweeps,” Garrett continued, adding that the authorities had been notified. 

Galaxy Digital’s research arm also wrote on X that the thief had an unusual pattern of moving the coins. 

“The pattern tells us these were all the same attacker — it does not capture the attack itself, which looks the same as if a coin owner chose to move coins,” the company said, adding that Bitcoiners should move funds out of single-signature Coldcard addresses and into secure custody.

After over $35 million in Bitcoin was drained from wallets on Thursday, Coinkite said that a firmware bug in Coldcard Mk3 devices — starting with version 4.0.1 in March 2021 — caused seed generation to fall back to a weak software Pseudorandom Number Generator instead of the hardware true random number generator. 

This allowed private keys for many single-signature wallets (especially those created without dice rolls or a strong BIP-39 passphrase) predictable enough for attackers to brute-force.

Later on Friday, Coinkite admitted all of its models were vulnerable following more thefts. Over $70 million has so far been swiped and engineers have warned that more Bitcoin addresses could be at risk. 

The company makes a number of Bitcoin products, including cold storage hardware wallets.