Technically you need 51% of all blackcoins to perform a hack in terms of double spending etc. Theoretically the required amount of coins is smaller if an attacker is able to precompute the chain, but this is open research afaik.
20% is enough to do double-spending attacks from time to time (like once per month) with no direct costs.
20% of active stakes at the moment off course, less active stakes, less security, less interest make less actives stakers
http://www.reddit.com/r/Bitcoin/comments/22aw8c/most_altcoins_are_not_secure_enough_they_exist/
Well this comment was related to PeerCoin and the actual statement is:
I haven't done analysis on 51% attack on ppc, and I really doubt 20% will be enough.
I don't want to say that you are wrong, but want to stress that these topics are very hot (and interesting) and not completely understood yet [edit: by the larger audience, brains like rat4 surely have a better understanding].
Thats Right, what make me think its that is only 20% of active stakes.
On LOW REWARD POS, less people gonna be willing to active stake,
Its just that in crypto security came from miners, less rewards to miners make less relaltive security
I think that this can be a problem just like for Doge is (low early pow reward) that can be BC problem (using analogy)
But unlike in Doge in PoS there is no real work that has to be done, so basically there is no reason not to stake as long as you have a device running that is able to stake. When did you switch off your mobile phone last time?