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Alerts: Update SPV Mining Alert
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harding committed Jul 6, 2015
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52 changes: 43 additions & 9 deletions _alerts/2015-07-04-spv-mining.html
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active: true
banner: "WARNING: many wallets currently vulnerable to double-spending of confirmed transactions (click here to read)"
---
{% capture markdown %}
<p><em>This document is being updated as new information arrives. Last
update: 2015-07-04 16:00 UTC</em></p>
update: 2015-07-06 02:00. All times are UTC.</em></p>

**Note: this alert is on-going: the situation has not yet been
resolved. ([Update #1](#update-1))**

{% assign confs="30" %}

<h2 id="summary">Summary</h2>

<p>Your bitcoins are safe if you received them in transactions confirmed before 2015-07-04 15:00 UTC.</p>
<p>Your bitcoins are safe if you received them in transactions confirmed before 2015-07-06 00:00 UTC.</p>

<p>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:</p>

<ul>
<li><b>Lightweight (<a href="http://bitcoin.stackexchange.com/questions/4649/what-is-an-spv-client">SPV</a>) wallet users</b> should wait an additional {{confs}}
confirmations more than you would normally wait.</li>
<li markdown="span"><b>Lightweight (<a href="http://bitcoin.stackexchange.com/questions/4649/what-is-an-spv-client">SPV</a>) wallet users</b> should wait an additional {{confs}}
confirmations more than you would normally wait. Electrum users,
please see [this note][electrum note].</li>

<li><b>Bitcoin Core 0.9.4 or earlier users</b> should wait an
additional {{confs}} confirmations more than you would normally
Expand Down Expand Up @@ -77,8 +82,21 @@ <h2 id="cause">What's Happening</h2>

<p>Summary: Some miners are currently generating invalid blocks. Almost
all software (besides Bitcoin Core 0.9.5 and later) will accept these
invalid blocks under certain conditions. The paragraphs that follow
explain the cause more throughly.</p>
invalid blocks under certain conditions.</p>

So far, the following forks of two or more blocks have occurred:

{% assign Blocks='Blocks <sup><a href="#invalid-blocks">[1]</a></sup>' %}

<a name="list-of-forks" />

| Start date | End time | {{Blocks}} | Double Spends |
|----------------|----------|------------|---------------|
| 4 July @ 02:10 | 03:50 | 6 | 0 |
| 5 July @ 21:50 | 23:40 | 3 | Not yet known |


The paragraphs that follow explain the cause more throughly.

<p>For several months, an increasing amount of mining hash rate has been
signaling its intent to begin enforcing <a
Expand All @@ -87,7 +105,7 @@ <h2 id="cause">What's Happening</h2>
once 950 of the last 1,000 blocks were version 3 (v3) blocks, all
upgraded miners would reject version 2 (v2) blocks.</p>

<p>Early morning UTC on 4 July 2015, the 950/1000 (95%) threshold was
<p>Early morning on 4 July 2015, the 950/1000 (95%) threshold was
reached. Shortly thereafter, a small miner (part of the non-upgraded
5%) mined an invalid block--as was an expected occurrence.
Unfortunately, it turned out that roughly half the network hash rate
Expand All @@ -106,14 +124,30 @@ <h2 id="cause">What's Happening</h2>
been downgraded to SPV-level security by the new BIP66 consensus
rules.</p>

<p>The immediate fix, which is well underway as of this writing, is to
<p>The recommended fix, which was attempted, was to
get all miners off of SPV mining and back to full validation (at
least temporarily). As this progresses, we will reduce our
least temporarily). If this happens, Bitcoin.org will reduce our
current recommendation of waiting {{confs}} extra confirmations to a
lower number.</p>

(**New 6 July 04:00**{:#update-1}) A new fork occurred starting 5 July at
21:30 with three blocks before the valid chain again became the
strongest chain. See the recently-added [list of forks](#list-of-forks).
Reports that the situation has past are **not correct.** Please continue
to wait {{confs}} more confirmations than you usually would wait before
accepting a transaction.

## Invalid Blocks

Please see the list of [invalid block hashes][] on the Bitcoin Wiki.

<!--
<div style="text-align:right">
<i>This notice last updated: 2015-07-04 06:00 UTC</i>
</div>
-->

[electrum note]: https://en.bitcoin.it/wiki/July_2015_Forks#Electrum
[invalid block hashes]: https://en.bitcoin.it/wiki/July_2015_Forks#Invalid_Block_Hashes
{% endcapture %}
{{ markdown | markdownify }}

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