WASHINGTON – When Microsoft introduces its long-awaited Windows Vista operating system this month, it will have an unlikely partner to thank for making its flagship product safe and secure for millions of computer users across the world: the National Security Agency.

For the first time, the giant software maker is acknowledging the help of the secretive agency, better known for eavesdropping on foreign officials and, more recently, U.S. citizens as part of the Bush administration’s effort to combat terrorism. The agency said it has helped in the development of the security of Microsoft’s new operating system – the brains of a computer – to protect it from worms, Trojan horses and other insidious computer attackers.

“Our intention is to help everyone with security,” Tony Sager, the NSA’s chief of vulnerability analysis and operations group, said Monday.

The NSA’s influence might be felt widely. Windows commands more than 90 percent of the worldwide market share in desktop operating systems, and Vista, which is set to be released to consumers Jan. 30, is expected to be used by more than 600 million computer users by 2010, according to Al Gillen, an analyst at market research firm International Data.

Microsoft has not promoted the NSA’s contributions, mentioning on its Web site the agency’s role only at the end of its “Windows Vista Security Guide,” which states that the “guide is not intended for home users” but for information and security specialists.