A software development toolset, VSTO is available in Microsoft’s Visual Studio IDE. It enables Office Add-In’s (a type of Office application extension) to be developed in .NET and also allows for Office documents to be created that will deliver and execute these Add-In’s.

In recent months, Microsoft has detected a wide range of social engineering campaigns using weaponized legitimate open-source software by an actor we track as ZINC. Microsoft Threat Intelligence Center (MSTIC) observed activity targeting employees in organizations across multiple industries including media, defense and aerospace, and IT services in the US, UK, India, and Russia. Based on the observed tradecraft, infrastructure, tooling, and account affiliations, MSTIC attributes this campaign with high confidence to ZINC, a state-sponsored group based out of North Korea with objectives focused on espionage, data theft, financial gain, and network destruction.