Google has returned fire at Microsoft, accusing its rival of resorting to false allegations in a battle to win a US government contract.

Microsoft recently suggested Google intentionally misled the U.S. government over its compliance with the Federal Information Security Management Act (FISMA). Microsoft claims Google filed a separate FISMA application for Google Apps for Government, then leaps to the conclusion that Google Apps for Government is not FISMA certified.

"These allegations are false. We take the federal government?s security requirements seriously and have delivered on our promise to meet them. What?s more, we?ve been open and transparent with the government, and it?s irresponsible for Microsoft to suggest otherwise," Google enterprise security director Eran Feigenbaum said in a blog post.

Last year, the Department of the Interior selected Microsoft offerings for its new cloud-based email system. In October, Google responded by suing the Government. Google announced its lawsuit with a proclamation of support for "open competition." It then touted the security benefits of Google Apps for Government. Google filed a motion for a preliminary injunction telling the court that Google Apps for Government is certified under FISMA.

Microsoft said documents unsealed in the court case showed that "Google Apps for Government," Google's Internet-based suite of office tools, had not been certified under the Federal Information Security Management Act (FISMA).

"We received FISMA authorization for Google Apps from the General Services Administration (GSA) in July 2010," Feigenbaum explained. "Google Apps for Government is the same technology platform as Google Apps Premier Edition, not a separate system. It includes two added security enhancements exclusively for government customers: data location and segregation of government data. In consulting with GSA last year, it was determined that the name change and enhancements could be incorporated into our existing FISMA certification. In other words, Google Apps for Government would not require a separate application," she added.

Feigenbaum said Google's veracity was backed by congressional testimony from the GSA on Tuesday.

"We've been very transparent about our FISMA authorization," she said.

"Our documentation has always been readily available for any government agency to review."