I suggest you look into what's called the '51% Attack' and 'Timewarp Exploit'. From what i've read, having over 50% of the network hash does not guarantee a successful attack, it only makes it more likely to be successful. Litecoin's fast block times also make it much less likely for the attack to be successful compared to BTC.
None of that is right. With a majority of the hashpower an attacker has a mathematical certainty of generating the longest chain. However an attacker would probably want a larger margin so there is more confidence over how long it takes for the attacker to come out ahead. A faster blocktime does not reduce the chance of success. A faster block time means a higher rate of orphans which means more of the legit miner's hashpower is wasted. An attacker is not subject to orphans as the attacker will always build only of his own chain.
That being said an entity simply having a majority isn't a guarantee there will be an attack.
