Microsoft has accused Google of lying about the level of security certification it received for a suite of office software produced for the United Stated federal government. The claim follows the release of documents from the Department of Justice that supposedly reject Google’s assertions that its “Google Apps for Government” software was certified under the Federal Information Security Management Act (FISMA). Google has countered that its apps are, in fact, certified.

　　According to a blog post by Microsoft Corporate Vice President & Deputy General Counsel David Howard, recently unsealed court documents reveal that “the United States Department of Justice had rejected Google’s claim that Google Apps for Government, Google’s cloud-based suite for government customers, has been certified under the Federal Information Security Management Act (FISMA).”

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　　Google responded to Microsoft’s claims, saying that its general business apps product, Google Apps for Business, received full FISMA certification, and was approved for used by the General Services Administration (GSA) in July 2010. While no FISMA certified on its own, Google Apps for Government is simply a version of Google Apps with increased security layers.

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　　“Google Apps received a FISMA security authorization from the General Services Administration in July 2010,” Google’s David Mihalchik told Fortune. “Google Apps for Government is the same system with enhanced security controls that go beyond FISMA requirements. As planned we’re working with GSA to continuously update our documentation with these and other additional enhancements.”

　　This spat, like nearly all quarrels between competing corporations, is about money.

　　Google is actively trying to displace Microsoft as the go-to company for government office software purchases — or at least break its stranglehold on that market, which has long been dominated by Microsoft. As the Los Angeles Times points out, building “a special, extra-secure” version of its enterprise office software is a key component to Google’s strategy in this area.

　　The DOJ court documents that revealed Google Apps for Government’s security clearance is part of ongoing litigation filed by Google in October against Microsoft after the Department of the Interior granted Microsoft with a contract to supply the DOI with email services.

　　Google has made some headway into the government market, however, with the GSA awarding Google with a $6.7 million contract in December to supply its more than 15,000 employees with Gmail, word processing and other office applications over the next five year.