Roughly 594 bitcoin, worth about $38 million, was swept from around 500 wallets in less than half an hour. That number is almost certainly going to grow. The apparent root cause is a catastrophic failure in Coldcard's seed-generation path. Mk3 devices running affected firmware may have generated seeds with an effective search space of roughly 40 bits. And in some cases were entirely deterministic. Coinkite now says seeds generated on Mk4, Q, and Mk5 firmware were also affected, with a maximum of about 72 bits of entropy instead of the intended 128, and a worst case scenario much lower. This is the only thing I am writing about this week because nothing else is remotely as important.
My current assessment is blunt: I would not consider funds secure in a wallet created on affected Coldcard firmware. For the most vulnerable Mk3 setups, assume the passphrase is the only meaningful barrier left unless you supplied substantial independent entropy when the seed was created. If you know you used 100 or more fair, private dice rolls, that materially changes the analysis. If you are unsure about the device, firmware, seed-generation method, or passphrase strength, treat the setup as vulnerable. Please remain calm but act quickly.
This is a terrible moment to choose and configure a permanent replacement cold-storage system. A rushed migration can create a second failure while you are trying to escape the first one. There is nothing wrong with temporarily parking bitcoin at a Bitcoin-only exchange you trust, or in a reputable Bitcoin-only hot wallet such as BlueWallet or Sparrow, while you make a deliberate long-term decision. The exchange route carries privacy and counterparty tradeoffs. The hot-wallet route creates a single point of failure on an internet-connected device. Neither is perfect. Both may be safer than leaving meaningful funds behind a seed whose entropy is now in question.
I am still developing my long-term recommendation and reviewing the available designs. My current direction is Bitkey for nontechnical users and SeedSigner for people prepared to handle a more technical setup. That recommendation may evolve as more research comes out. If you believe your setup may be vulnerable, do not hesitate to reach out today or over the weekend. I will be monitoring this closely, and I know many other people in the Bitcoin community will be doing the same. If you were affected, I am so incredibly sorry.