This is now fixedEdited by @StephanTual Thursday 7pm GMT.
This issue only affected geth users (or geth users in combination with ethminer). If you are using Geth, please update now.
If using the PPA:
sudo apt-get update
sudo apt-get upgrade
If using brew:
brew reinstall ethereum
If using a windows binary: download the updated binary
If you are building from source:
(you need to be on the Master branch)
The correct version for this update on Ubuntu AND OSX is Geth/v1.0.2-4591ae56 and v1.0.2-a0303f (both are fine)
On windows, the latest chocolatey package version is Geth Stable 188.8.131.52 and it's pulling from download/v184.108.40.206/Geth-Win64-20150820212541-1.0.1-f0c7af0.zip (this is normal)
Note, if you are getting:
I0820 19:00:53.368852 4539 chain_manager.go:776] Bad block #116522 (05bef30ef572270f654746da22639a7a0c97dd97a7050b9e252391996aaeb689)
I0820 19:00:53.368891 4539 chain_manager.go:777] Found known bad hash in chain 05bef30ef572270f654746da22639a7a0c97dd97a7050b9e
.. after updating this is NORMAL and will resolve itself once your peers have updated their clients, too.
UPDATE 10:52 BST: We have released a new update on the state of the network post consensus failure and expectations on chain reorganization depth (now 750 blocks) https://blog.ethereum.org/2015/08/20/security-alert-consensus-issue/
This alert is related to a consensus issue that occurred on the Frontier network at block 116,522, mined on 2015-08-20 at 14:59:16+02:00
Issue description: Edge case in the Go implementation of the consensus protocol for contract suicides
Affected implementations: All implementations of Geth (Go). Eth (C++) and pyethereum (Python) are unaffected
Effects on expected chain reorganisation depth: Increase waiting time for eventual block confirmation to 12 hours