A .NET toolset is software built using Microsoft’s .NET platform and its libraries. In cybersecurity, the phrase can describe malware whose components are written for .NET. Such programs may be easier for their authors to develop, update, or extend, and can use modular designs that load additional components after initial execution.
In the article’s context, DarkVigil is described as a modular .NET toolset, also known as FDMTP. That description identifies its technology and design, but does not establish which capabilities were used or what data, if any, was taken. Defenders can look for unusual .NET processes, unexpected module loading, and suspicious network or configuration activity. Because .NET is also widely used for legitimate applications, these indicators need to be assessed in context rather than treated as proof of malware.