Amazon CEO Jeff Bezos. Reuters The CIA is on the verge of signing a cloud computing contract with Amazon, worth up to $600 million over 10 years, reports Frank Konkel at Federal Computer Week.

If the details about this deal are true, it could be a game-changer for the enterprise cloud market.

That's because Amazon Web Services will help the CIA build a "private cloud" filled with technologies like big data, reports Konkel, citing unnamed sources.

The CIA is pretty closed-lipped about its business, as spies are apt to be. This is no exception. It won't confirm the deal or comment on it, so details are sketchy. But the contract is expected to be for a "private" cloud, which is not what AWS is known for.

AWS is the largest "public" cloud provider. In general, the term "private cloud" means using cloud computing technologies in a company's own data center. Public clouds are in hosted facilities, where the hardware is shared with many users. Sharing the hardware saves money.

Amazon hasn't been very interested private clouds. Years ago, it even argued against them. If companies want private clouds based on Amazon's tech, they often go to startups like Eucalyptus Systems.

Amazon's approach has been its "Virtual Private Cloud." This still uses hardware hosted by Amazon, but adds extra security to make it behave more like a private datacenter.

If Amazon were really to enter the private cloud business, this could be a big threat to VMware and Citrix, the two biggest players in this market. (Also to HP, IBM, Cisco, and other hardware vendors pushing private clouds.)

Whether Amazon has had a massive change of heart about private clouds or not, gaining the CIA as a customer is a major coup. Competitors like IBM, HP, and Rackspace say their clouds are more reliable and far more secure than Amazon's.

Looks like the CIA disagrees.

We reached out to Amazon for comment but have not yet heard back.