Eventually after accumulating enough “old stake”, the user can begin creating blocks and destroying as many or more coin days than the network was at that time.
This block generation can be repeated until it catches up to and beats the current main-chain very cheaply. There are also “stake grinding” attacks which require a trivial amount of currency.
In a stake  grinding attack, the attacker has a small amount of stake and goes through the history of the blockchain and finds places where their stake wins a block. In order to consecutively win, they modify the next block header until some stake they own wins once again.
This attack requires a bit of computation, but definately isn’t impractical. Because these attacks exists, including Peercoin  and Blackcoin  proof of stake cryptocurrencies have “master” public keys that control the blockchain. This class of cryptocurrency is either insecure or centralized, however proof of stake based on a PoW currency is useful in some systems because gaining stake is costly, but it isn’t workable for bootstrapping distributed consensus.
It is an application layer protocol and tools can be built on it like websites can be built on HTTP. There is a class of cryptocurrencies that promise features like casino websites and exchanges and anonymity protocols to be built on top of them.
When creating a new website, one doesn’t make a new protocol unless it is necessary. When creating an app such as ” DarkSend “, one doesn’t need to make a new protocol such as “Darkcoin”.
USE OF INFORMATION
Because Darkcoin is by far the most popular cryptocurrency of this class, the Darkcoin example will be covered in this section. The Darkcoin devs created a tool called DarkSend. New coins can be created through regular mining or minting process where people get rewards from the coins they hold.
New faucets within few days!
INFORMATION WE COLLECT
It was first released in Oct by a former Google employee Charles Lee. It has been said that Litecoin is the first and only true alt coin ever built. Although there has been several successful coins made after Litecoin there are always special bond between Bitcoin and Litecoin as they are the biggest and most accepted coins and also technically nearly identical.
If you want to “play safe” then investing in Litecoin should be always your second best choice. Litecoin differs from Bitcoin in three ways: Litecoin uses scrypt algorithm instead of Bitcoins SHA which was designed to eliminate the use of typical ASIC miners and make it more profitable for users with regular computing hardware.