SAN FRANCISCO - Microsoft Corp found a new way to lash out at Google Inc on Monday, extending the hostilities between two of the most prominent corporations in the technology industry.

Microsoft claimed Google has been misleading customers about the security certification of its suite of software programs for governments.

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Microsoft's deputy general counsel, David Howard, blogged on Monday about a newly unsealed court document that shows that "Google Apps for Government" hasn't been certified under the Federal Information Security Management Act. Google's website claims it has, and the company has attested to that in court documents.

"It's time for Google to stop telling governments something that is not true," Howard wrote.

The documents are part of a Google lawsuit alleging that it was improperly frozen out of competing for a US Department of Interior contract to build a new e-mail system for 85,000 employees -- a contract Microsoft won. A judge earlier sided with Google's belief that the bidding was rigged to favor Microsoft, and issued a preliminary injunction with the two sides duke it out.

Google insists it's not deceiving anyone, since a less-robust version of the product has already been certified under FISMA.

"We did not mislead the court or our customers," the company said in a statement, noting that "Google Apps" received a FISMA clearance in July 2010, and that "Google Apps for Government" is "the same system with enhanced security controls that go beyond FISMA requirements."

The documents show that Google is in the process of applying for certification for "Google Apps for Government."

The controversy illustrates the wide range of complaints and tactics Google and Microsoft are using to attack each other. Their enmity has grown as Microsoft encroaches on Google's search turf and Google goes calling on Microsoft's customers to sell them programs such as email and word processing.

The maneuvering has ranged from a "gotcha"-type stunt in which Google accused Microsoft in February of copying Google's search results, to Microsoft -- long a target of antitrust complaints -- filing its first formal antitrust complaint against a rival by arguing to European authorities that Google is abusing its dominance to freeze out rival services.