user13087: I'm discovering alt-coins.
Now, I'm on piratecoin.
{
    "blocks" : 34167,
    "currentblocksize" : 1225,
    "currentblocktx" : 1,
    "difficulty" : 0.14348426,
    "errors" : "",
    "generate" : true,
    "genproclimit" : -1,
    "hashespersec" : 355,
    "networkhashps" : 11127177,
    "pooledtx" : 1,
    "testnet" : false
}

There is somehow calculated networkhashps, seems it is aproximation from difficulty, it is 11,127,177, ~ 11mh/s. I'm count on my own, 350h/s, however, cgminer show me 180Kh/s. Probably it doesn't counts in getmininginfo or recalculated somehow. Anybody?
I've seen persons with much greater speed, its called mining rig. 20-30 may be 100 GPU in a bunch. 
What if such huge miner connect to such young alt-coin network, download whole of current blockchain, and start mining off-line. After 5 hours he come back to network, his blockchain will be with bigger difficulty. 
Can he attack network in such way?

user85: Absolutely. When a coin is secured by proof of work, if there is insufficient proof of work, the coin is not secure.

13087: <p>I'm discovering alt-coins.</p>

<p>Now, I'm on <a href="https://cryptocointalk.com/topic/3054-piratecoin-ptc-information/" rel="nofollow">piratecoin</a>.</p>

<pre><code>{
    "blocks" : 34167,
    "currentblocksize" : 1225,
    "currentblocktx" : 1,
    "difficulty" : 0.14348426,
    "errors" : "",
    "generate" : true,
    "genproclimit" : -1,
    "hashespersec" : 355,
    "networkhashps" : 11127177,
    "pooledtx" : 1,
    "testnet" : false
}
</code></pre>

<p>There is somehow calculated <code>networkhashps</code>, seems it is aproximation from <code>difficulty</code>, it is 11,127,177, ~ 11mh/s. I'm count on my own, <code>350h/s</code>, however, <code>cgminer</code> show me <code>180Kh/s</code>. Probably it doesn't counts in <code>getmininginfo</code> or recalculated somehow. Anybody?</p>

<p>I've seen persons with much greater speed, its called mining rig. 20-30 may be 100 GPU in a bunch. </p>

<p>What if such huge miner connect to such young alt-coin network, download whole of current blockchain, and start mining off-line. After 5 hours he come back to network, his blockchain will be with bigger <code>difficulty</code>. </p>

<p>Can he attack network in such way?</p>
 85: <p>Absolutely. When a coin is secured by proof of work, if there is insufficient proof of work, the coin is not secure.</p>
