A number of cloud services offered by the Redmond software giant use the MFA offered by Azure Active Directory to authenticate by default.

The Azure status page indicates that the issue began at 14.25 UTC on Tuesday (1.30am AEDT on Wednesday), when customers started experiencing difficulty signing into resources offered via Azure.

The company says the severity of the problem lessened by 17.08 UTC on Tuesday (4.08am AEDT Wednesday).

"After a preliminary investigation, engineers found that an earlier DNS issue triggered a large number of sign-in requests to fail, which resulted in backend infrastructure becoming unhealthy," the company said.

"After the DNS issue was resolved, engineers then focused on cycling the relevant backend services to resolve the congestion issue. They observed a decrease in the failure rate after the reboot cycles.

"Engineers continue to monitor overall platform health and prevent future occurrences. A full Root Cause Analysis will be made available within 72 hours."

On Tuesday AEDT, Microsoft faced issues with its Exchange Online service, with a number of products being affected.

Last week's 19-hour MFA issue was resolved by the company resorting to an age-old remedy that has been used for Windows systems – rebooting.