So I was looking at the new PoW data at https://dcrstats.com/pow (very cool btw) and I noticed that at the time I viewed it the SuprNova pool was 47.1% of the total network has rate. I remember Bad Things could happen in Bitcoin if one pool controlled over half the hash rate. Does the same apply to Decred or are there checks to stop that being an issue (i.e. PoS). I think I recall reading something about it but can't recall where.
The threat of a 50% mining pool is that if the pool agrees to it, they can then attempt a 51% attack, which is basically where, since they now have the majority (not just plurality, actual majority), they have a fair amount of sway in dictating which blocks get added to the network or not. This isn't ironclad, of course. Owning 50% of the hashing power gives you a 50% chance to find a given block, but to make a significant impact you still really need to find multiple consecutive blocks. This is why Bitcoin suggests 6 confirmations: to keep a transaction hidden from the network, someone would then have to exclude it for 6 consecutive blocks, and while the first block had a 50% chance, that chance goes down exponentially for each additional block the network needs to find. A 50% mining network would have a 1/64 chance of finding 6 consecutive blocks, so this is considered more or less safe, though there are suspicions that an organization does have the power to pull it off. Keep in mind that if Google turned all of their corporate computational power to Bitcoin hashing, they would amount to less than statistical noise. Decred attempts to mitigate this with Proof Of Stake mining. When the Testnet was first launched, I was playing around and, misunderstanding the outputs in cgminer, jokingly commented "Behold my 51% attack" in the IRC thread. Jolan (I believe) responded with "I'll just vote against all of your blocks," and this is where the advantage of Proof Of Stake comes in. As was commented in the thread I linked above, to run a 51% attack on Decred, you would really need 51% of the hashing power AND access to 51% of the voting tickets, and PoS voting is so simple (ticket prices notwithstanding, you can get started for less than $40US, and that's if you buy a Raspberry Pi and follow my tutorial, I believe Amazon VPS services are even cheaper to get into) that owning 51% of the voters is phenomenally more difficult than just 51% of the miners.
Realistically, to make any significant impact you'd need even more than 51% of the total tickets since each block requires 3/5 votes and so you'd need to win those votes on multiple consecutive blocks. As you can imagine, the chances of this happening are incredibly tiny after a few blocks.
And lastly if a pool would pull this off the reputation which was build over years would be killed within seconds...
Sorry @ocminer, didn't mean to imply that the pool would do such a thing, it was just used an example since it's what I saw. The question itself was mostly academic. I was just curious as to the possibility of such a thing (by any group/pool, not just suprnova) and the safeguards built into Decred.