In brief

COLDCARD Mk3 Security Advisory

If you generated a seed on a Mk3 after firmware 4.0.1, your funds may be at risk.

Mk4, Q and Mk5 are not affected based on our early analysis.

Read the advisory and migrate carefully:https://t.co/3vgPHOjMS7

— COLDCARD (@COLDCARDwallet) July 30, 2026

What went wrong

What owners must do

1/ Earlier today, our Bitcoin engineering and security teams at Block began investigating reports of non-Bitkey wallets being drained. To proactively protect our customers, we began investigating immediately. Here’s what we found 🧵

— Max Guise (@max_guise) July 31, 2026