Since the dominant pool (foundrydigital.com) only has 28.4% of the network, they can't do the 50% attack, given if the second biggest pool decides to work with them they will have 49.8% of the network, so, not enough to manipulate the blocks.
The more hash power a mining pool owns, the more chance they have to replace an existing block with a new one. This doesn't mean the mining pool have to own more than 50% of the total hash power to do so. Any mining pool can try to perform such an attack even with less than 50 % of the total hash power.