This document is being updated as new information arrives. Last update: 2015-07-15 13:00. All times are UTC.

Note: this situation has not been fully resolved, and it does not appear that it will be fully resolved anytime soon. Users of the affected wallets listed below are still advised to wait additional confirmations or to switch to a safer wallet.

Summary

Your bitcoins are safe if you received them in transactions confirmed before 2015-07-15 12:00 UTC.

However, there has been a problem with a planned upgrade. For bitcoins received later than the time above, confirmation scores are significantly less reliable then they usually are for users of certain software:

  • Lightweight (SPV) wallet users should wait an additional 30 confirmations more than you would normally wait. Electrum users, please see this note.
  • Bitcoin Core 0.9.4 or earlier users should wait an additional 30 confirmations more than you would normally wait or upgrade to Bitcoin Core 0.10.2.
  • Web wallet users should wait an additional 30 confirmations more than you would normally wait, unless you know for sure that your wallet is secured by Bitcoin Core 0.9.5 or later.
  • Bitcoin Core 0.9.5 or later users are unaffected. (Note: upgrade to 0.10.2 is recommended due to denial-of-service vulnerabilities unrelated to this alert.)