A firmware flaw in Coldcard, a Bitcoin-only hardware wallet, has been linked to a $70.2 million Bitcoin theft. An attacker exploited a March 2021 firmware integration error that routed seed generation to a deterministic software pseudorandom number generator (PRNG). This allowed the attacker to drain 1,196 Bitcoin addresses in just 41 minutes on July 30. The incident highlights the critical importance of robust randomness in cryptographic key generation for hardware security devices.