Complex sentence: Similarly to Bitcoin, Litecoin can be attacked by an entity that can match or exceed the hash rate of the network, though such a 51% attack becomes more difficult to launch and maintain as the hash rate of the network grows.
Split into simpler sentences: Similarly to Bitcoin, Litecoin can be attacked by an entity that can match or exceed the hashrate of the network. Such a "51% attack" becomes more difficult to launch and maintain as the hash rate of the network grows.