A .csproj file is the XML project file used by Microsoft Build Engine (MSBuild) to define how a .NET application is compiled, packaged, and published. It lists source files, references, target frameworks, and build settings, and it can also import other build logic from .props and .targets files.
Because MSBuild can run tasks during a build, a malicious or tampered .csproj file can be more than configuration. It may trigger commands, load unexpected targets, or change the build flow so code executes when a developer opens or builds the project. That makes project files a real attack surface in software supply-chain and phishing scenarios. Defenders should review unfamiliar projects in isolated environments, inspect imports and custom targets, and watch for suspicious Exec tasks, scripts, or package references that do not match normal development work.