Alert system

Bitcoin versions 0.3.10 and later have an alert system which allows messages about critical network problems to be broadcast to all clients. When an alert is in effect, the message it contains will appear in the status bar of all clients, in the "errors" field of RPC getinfo, and will notify any script registered with Bitcoin-Qt/bitcoind -alertnotify command-line option.

Alert message

Alerts are broadcast using the same TCP relay system as block and tx messages. They are not encoded in a special transaction. Unlike block and tx relaying, alerts are sent at the start of every new connection for as long as the alert is in effect. This ensures that everyone receives the alert.

Alerts contain this information:

• How long to relay the alert.
• How long to consider the alert valid.
• An alert ID number.
• A list of alerts that should be canceled upon receipt of this alert.
• Exactly which versions of Bitcoin are affected by the alert. Unaffected versions still relay the alert for the benefit of older versions.
• Alert priority.
• The alert text.

Only alerts that are signed by a specific ECDSA public key are considered valid. The known private key holders are Satoshi Nakamoto, Gavin Andresen and theymos. There are other people able to issue alerts in the event of the incapacitation of the aforementioned.

Safe mode

Until version 0.3.20, Bitcoin went into safe mode when a valid alert was received. In safe mode, all RPC commands that send BTC or get info about received BTC return an error. Current Bitcoin versions no longer go into safe mode in response to alerts, though Bitcoin will still go into safe mode when it detects on its own that something is seriously wrong with the network.

Even though Bitcoin no longer automatically disables RPC when an alert is live, it is wise for Bitcoin sites to shut down when an alert has been issued. To detect an active alert, poll the "errors" field of getinfo.

To test safe mode, run Bitcoin with the -testsafemode switch. To override a real safe mode event, run Bitcoin with the -disablesafemode switch.

Past alerts

ID	Sent date	Expires (UTC)	Versions	Priority	Message
1010	Feb 18, 2012	Feb 21 02:47:15	All	100	See bitcoin.org/feb20 if you have trouble connecting after 20 February
1011	Mar 16, 2012	cancelled May 15, 2012	0.5 - 0.5.3	5000	URGENT: security fix for Bitcoin-Qt on Windows: http://bitcoin.org/critfix
1012	Mar 16, 2012	cancelled May 15, 2012	6.0	5000	URGENT: security fix for Bitcoin-Qt on Windows: http://bitcoin.org/critfix
1013	Mar 16, 2012	cancelled May 15, 2012	5.99	5000	URGENT: security fix for Bitcoin-Qt on Windows: http://bitcoin.org/critfix
1015	May 15, 2012	May 16, 2013	0.1 - 0.4.5	5000	URGENT: upgrade required, see http://bitcoin.org/dos for details
1016	May 15, 2012	May 16, 2013	0.4.99 - 0.5.4	5000	URGENT: upgrade required, see http://bitcoin.org/dos for details
1020	May 15, 2012	May 16, 2013	0.6.0	5000	URGENT: upgrade required, see http://bitcoin.org/dos for details
1032	March 12, 2013	March 13, 2013	0.8.0	5000	URGENT: chain fork, stop mining on version 0.8
1033	March 19, 2013	March 20, 2013	0.1 - 0.7.2	10	See http://bitcoin.org/may15.html for an important message
1034	May 9, 2013	June 8, 2013	0.1 - 0.7.2	10	Action required: see http://bitcoin.org/may15.html for more information
1040	April 11, 2014	cancelled	0.9.0	5000	URGENT: Upgrade required: see https://www.bitcoin.org/heartbleed/
1041	April 11, 2014	April 11, 2015	0.9.0	5000	URGENT: Upgrade required: see https://www.bitcoin.org/heartbleed