DEV-0343 is a new activity cluster that the Microsoft Threat Intelligence Center (MSTIC) first observed and began tracking in late July 2021. MSTIC has observed DEV-0343 conducting extensive password spraying against more than 250 Office 365 tenants, with a focus on US and Israeli defense technology companies, Persian Gulf ports of entry, or global maritime transportation companies with business presence in the Middle East. Less than 20 of the targeted tenants were successfully compromised, but DEV-0343 continues to evolve their techniques to refine its attacks. MSTIC noted that Office 365 accounts with multifactor authentication (MFA) enabled are resilient against password sprays.
Microsoft uses DEV-#### designations as a temporary name given to an unknown, emerging, or a developing cluster of threat activity, allowing MSTIC to track it as a unique set of information until they can reach high confidence about the origin or identity of the actor behind the operation. Once it meets the criteria, a DEV is converted to a named actor. As with any observed nation state actor activity, Microsoft has directly notified customers that have been targeted or compromised, providing them with the information they need to secure their accounts.
Source: Microsoft Threat Intelligence Center