Solidcoin takes the following approach to preventing the 51% attack:
As with existing cryptocurrencies, SolidCoin 2.0 stores transactions in a "block chain" which is essentially what it sounds like. Transactions go into a block, nodes do work on that block to verify it, and if the work is good enough they can submit it to the rest of the network. SolidCoin 2.0 then comes into action, every other block in the chain must be worked on by someone with at least a million (1,000,000) SolidCoins in an account.
One initial problem with this p2p security feature is SolidCoin only had 1.112 million coins prior to this security feature being implemented. To solve this, 10 accounts of 1.2 million were created in the genesis block. These are special accounts that cannot be spent on the network, effectively making them "Null accounts used for special purposes", until SolidCoin does have real millionaires.
So, who controls these ten special purpose accounts? And are they supposed to be disbanded when real millionaires come around?