“If you have computers chugging away as bitcoin mining machines, don’t be surprised if your output just fell through the floor. Reuters notes that code built into the digital currency system has cut the mining reward in half as of July 9th. Where there were previously 25 bitcoins (roughly $16,000) to be mined every 10 minutes, you now have to fight over 12.5. The measure automatically kicks in every four years as part of an attempt to curb inflation that would come from both a growing number of miners and ever-faster computers.”
Source: Bitcoin mining just became less rewarding, on purpose