about POW here
Code:
bytes32 public currentChallenge; // The coin starts with a challenge
uint public timeOfLastProof; // Variable to keep track of when rewards were given
uint public difficulty = 10**32; // Difficulty starts reasonably low
function proofOfWork(uint nonce){
bytes8 n = bytes8(sha3(nonce, currentChallenge)); // Generate a random hash based on input
require(n >= bytes8(difficulty)); // Check if it's under the difficulty
uint timeSinceLastProof = (now - timeOfLastProof); // Calculate time since last reward was given
require(timeSinceLastProof >= 5 seconds); // Rewards cannot be given too quickly
balanceOf[msg.sender] += timeSinceLastProof / 60 seconds; // The reward to the winner grows by the minute
difficulty = difficulty * 10 minutes / timeSinceLastProof + 1; // Adjusts the difficulty
timeOfLastProof = now; // Reset the counter
currentChallenge = sha3(nonce, currentChallenge, block.blockhash(block.number - 1)); // Save a hash that will be used as the next proof
}