Google has returned fire at Microsoft, accusing its rival of resorting to false allegations in a battle to win a US government contract.
"We take the federal government's security requirements seriously and have delivered on our promise to meet them," Google enterprise security director Eran Feigenbaum said in a blog post.
"What's more, we've been open and transparent with the government, and it's irresponsible for Microsoft to suggest otherwise."
Feigenbaum's message came two day after Microsoft hit Google with an accusation of issuing misleading claims.
Google rejected the charges by the Seattle-based software giant in the legal tussle over a nearly $60 million contract with the US Department of Interior.
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).
"Given the number of times that Google has touted this claim, this was no small development," Microsoft deputy general counsel David Howard said in a blog post.
"It's time for Google to stop telling governments something that is not true."
FISMA lays out the security standards for information management systems such as email.
Google and Onix Networking Corp., a reseller of Google products, filed suit against the US government last year claiming the terms for the Department of Interior contract favoured Microsoft.
Google argued that the terms of the bid for an email, calendar and document collaboration system for some 88,000 Interior Department employees implicitly rule out a Google product and favoured one from Microsoft.
Google was promoting Google Apps for Government for the contract over Microsoft's solution.
Google remained adamant that a version of Google Apps received a FISMA security authorization from the General Services Administration (GSA) in July 2010.
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."
Relations between the technology giants have become increasingly acrimonious of late and Microsoft last month joined an anti-trust complaint in Europe against Google over its Internet search.
In February, Google accused Microsoft's search engine Bing of copying its results.