Washington, DC (CNN Business) The National Security Agency recently alerted Microsoft to a major flaw in its Windows operating system that could let hackers pose as legitimate software companies, agency officials said on Tuesday.

Microsoft MSFT patches. issued a software update on Tuesday to fix the vulnerability, as part of its normal schedule for releasing softwarepatches.

News of the vulnerability and patch were first reported by independent journalist Brian Krebs, who said Microsoft provided its software fix to the military and key infrastructure companies ahead of Tuesday's public release.

Microsoft said in a statement Monday night that it provides advance versions of its updates to some users under a special testing program. Jeff Jones, a senior director at Microsoft, declined to discuss specifics of the flaw "to prevent unnecessary risk to customers."

The company did not immediately respond to a request for comment on Tuesday.

Read More