Why on earth would you halve the rewards? Belay that and focus on security. Someone with either epic hashrate (more than all alt's combined) is toying with the coin, or it's someone attacking the network itself.
I am not sure who is doing this but its probably
https://bitcointalk.org/index.php?topic=504103.0He was set out to destroy aurora and he managed to time warp it initiating the need for a fix. I am assuming since this is the only individual set on this mission from before and successfully doing it, its him again.