user38618: Years ago, GHash.io had claim of 40% of the network hashpower. They were close to 51%, where they would have the power to initiate a 51% attack. Now it has 0.2%. How did this happen?

user21017: Apparently they were hit with a massive denial of service attack in response to their growing hash rate. That combined with a subsequent drop in the price lead them to stop their cloud mining operation and focus on their exchange (cex.io).
The other non cloud-miners who left the pool most likely did it in response to the massive appeal from the community to find another pool.

38618: <p>Years ago, GHash.io had claim of 40% of the network hashpower. They were close to 51%, where they would have the power to initiate a 51% attack. Now it has 0.2%. How did this happen?</p>
 21017: <p>Apparently they were hit with a <a href="https://blog.cex.io/news/official-statement-on-the-last-weeks-ddos-attack-against-ghash-io-mining-pool-14156" rel="nofollow noreferrer">massive denial of service attack</a> in response to their growing hash rate. That combined with a subsequent drop in the price lead them to <a href="https://www.cryptocoinsnews.com/ghash-cex-scaling-back-mining-pool" rel="nofollow noreferrer">stop their cloud mining operation</a> and focus on their exchange (cex.io).</p>

<p>The other non cloud-miners who left the pool most likely did it in response to the massive appeal from the community to <a href="https://bitcointalk.org/index.php?topic=406541.0" rel="nofollow noreferrer">find another pool</a>.</p>
