This article originally appeared on ZDNet.

A number of Microsoft Azure and Office 365 users have been unable to get into their accounts for most of the day on November 19. The problem: A multi-factor authentication issue which hit users worldwide and left them unable to sign into their services.

The Office 365 status page noted that affected users may be unable to sign in using multi-factor authentication (two-factor authentication) and may also be unable to do self-service password resets.

“A subset of users are no longer receiving prompts on their mobile devices (SMS, call or push) and (we) are investigating diagnostic logs to understand why,” the status dashboard noted.

SEE: Electronic communication policy (Tech Pro Research)

Azure and Office 365 MFA services were affected starting at 4:39 am UTC, which was 4:39 a.m. ET, according to the Office status page.

The Azure status page noted that those affected may have had problems signing into Azure resources like Azure Active Directory, when MFA was required.

Azure engineers reported around noon ET today that they had deployed a hotfix , but that it took time to take effect across impacted reasons, and in particular Europe and Asia-Pacific. Engineers were reporting they have seen a reduction in authentication errors as a result of the hotfix. The hotfix also tipped off engineers that some subset of customers were not receiving SMS, Call or Push prompts for MFA.

“Engineers are continuing to explore additional workstreams and potential impact to customers in other Azure regions to fully mitigate this issue,” the Azure status page noted.

Beyond those status reports, Microsoft hasn’t shared information as to what caused the MFA services problem today.