The Government Accountability Office has sided with Microsoft in its challenge to a multibillion-dollar National Security Agency cloud computing contract that was originally awarded to rival Amazon Web Services.

In a decision filed late last week, the Government Accountability Office mandated that the NSA re-evaluate its decision to award a secret $10B contract, codenamed "WildandStormy," to AWS, Data Center Dynamics reports.

While details underlying the GAO’s ruling — as well as any specifics about the nature of WildandStormy itself — have been withheld by the agency as classified and proprietary information. The decision comes after Microsoft filed a challenge in late July, two weeks after the NSA awarded the contract to AWS.

"GAO found certain aspects of the agency’s evaluation to be unreasonable and, in light thereof, recommended that NSA reevaluate the proposals consistent with the decision and make a new source selection determination," said Ralph O. White, managing associate general counsel for the Procurement Law Division at GAO, according to Data Center Dynamics.

"GAO’s decision expresses no view as to the relative merits of the AWS and Microsoft proposals."

While Amazon could appeal the GAO’s ruling to the U.S. Court of Federal Claims, the potential length of such litigation could make that course of action unlikely, Data Center Dynamics reports.

According to Nextgov, the disputed cloud contract is likely an attempt to modernize the NSA’s repository of classified data, known as the Intelligence Community GovCloud. While the NSA operates three known data centers in Utah, Denmark and the United Kingdom, the signals intelligence and surveillance agency is joining the rest of the U.S. intelligence apparatus in an effort to switch from self-operated data storage and processing to cloud-based systems run by commercial providers, Nextgov reports.

WildandStormy is the second publicly known multibillion-dollar cloud computing contract awarded by U.S. intelligence agencies in the past year. Last November, the CIA decided to split its C2E cloud contract between five providers: AWS, Microsoft, Google, Oracle and IBM.

The dispute over WildandStormy is not the first time that Microsoft and AWS have butted heads over a national defense cloud contract in recent months. In July, Amazon’s legal challenges to the Department of Defense’s selection of Microsoft for its $10B JEDI initiative led the Pentagon to scrap the program altogether. The military’s new digital transformation effort, known as Joint Warfighter Cloud Capability, will be executed jointly by the two companies.

These conflicts reflect the growing importance of government contracts, both military and civilian, for hyperscale cloud providers and other data center operators. According to CBRE’s North American Data Center Trends Report, the increased need for cloud capacity by the U.S. federal government was one of the key contributors to the growth of cloud and colocation requirements across several markets.