Greenpeace took aim at Apple, Microsoft and Amazon over how the companies are powering the data centers that house their fast-growing cloud computing infrastructures. In a move that is reminiscent of its tussle with Facebook over its first-ever data center build in Prineville, Ore., Greenpeace has zeroed in on clean energy's boogeyman, coal. "Apple, Amazon and Microsoft are powering their growing 21st-century clouds with dirty, 19th-century coal energy," writes Greenpeace campaigner, Casey Harrell on the group's website. Not all big cloud computing companies are guilty of the same. In the organization's "How Clean is Your Cloud?" report (PDF), Facebook, Google and Yahoo! are hailed for their efforts to power their clouds from renewal energy sources.