user78: I don't understand this post.
What is "ArtForz modified exploit"?
What does "Gavin's patch will not work for the exchanges" mean?
Any more important details I'm missing?

user196: The answer to the title question "Why is BitcoinEXress planning a 51% attack on Namecoin?" has been given in the linked post itself:

Goals

Developing protection for Bitcoin against exploits
Developing a lethal alt chain killer.
Making developers aware that when the "bad guys" make you aware of an exploit, FIX IT!


We know the 51% attack could be a danger to bitcoin (there are several threads about this IIRC), so they are trying that attack against a bitcoin weaker clone to see "live" if it really works, to raise public awareness of this problem.

user365: This post by ArtForz on the forums explains the attack:
https://bitcointalk.org/index.php?topic=43692.msg521772#msg521772
Quote: "By exploiting the fact that retargeting ignores one block interval every period, it's possible for an attackers' fork chain to "jump backwards in time" and create lots of blocks at low difficulty without running nTime off into the far future."
This attack has been proven to work on GeistGeld (which uses 10 second blocks and 16 block retarget intervals). It was rather easy there, because of the low intervals and because the developers "forgot" to adjust other constants regarding timing and clocks. They since made it much better.
Now it seems it will be tried on namecoin, with the goal of making bitcoin more secure.

78: <p>I don't understand <a href="https://bitcointalk.org/index.php?topic=43465.msg521136#msg521136" rel="nofollow">this post</a>.</p>

<p>What is "ArtForz modified exploit"?</p>

<p>What does "Gavin's patch will not work for the exchanges" mean?</p>

<p>Any more important details I'm missing?</p>
 196: <p>The answer to the title question <em>"Why is BitcoinEXress planning a 51% attack on Namecoin?"</em> has been given in the linked post itself:</p>

<blockquote>
  <p>Goals</p>
  
  <ol>
  <li>Developing protection for Bitcoin against exploits</li>
  <li>Developing a lethal alt chain killer.</li>
  <li>Making developers aware that when the "bad guys" make you aware of an exploit, FIX IT!</li>
  </ol>
</blockquote>

<p>We know the 51% attack could be a danger to bitcoin (there are several threads about this IIRC), so they are trying that attack against a bitcoin weaker clone to see "live" if it really works, to raise public awareness of this problem.</p>
 365: <p>This post by ArtForz on the forums explains the attack:</p>

<p><a href="https://bitcointalk.org/index.php?topic=43692.msg521772#msg521772">https://bitcointalk.org/index.php?topic=43692.msg521772#msg521772</a></p>

<p>Quote: "By exploiting the fact that retargeting ignores one block interval every period, it's possible for an attackers' fork chain to "jump backwards in time" and create lots of blocks at low difficulty without running nTime off into the far future."</p>

<p>This attack has been proven to work on GeistGeld (which uses 10 second blocks and 16 block retarget intervals). It was rather easy there, because of the low intervals and because the developers "forgot" to adjust other constants regarding timing and clocks. They since made it much better.</p>

<p>Now it seems it will be tried on namecoin, with the goal of making bitcoin more secure.</p>
