Microsoft Threat Modeling Tool 2014

The Microsoft Threat Modeling Tool helps engineers analyze the security of their systems to find and address design issues early in the software lifecycle.
The Microsoft SDL Threat Modeling Tool is a core element of the SDL. The Microsoft Security Development Lifecycle (SDL) specifies development teams, should define a products default and a maximum attack surface during the design phase and reduce the likelihood for exploitation wherever possible.

The tool is used during the design phase of the SDL and helps architects and engineers analyze their designs and software architecture before they start implementation.