“You shouldn’t write software to use .NET. No exceptions,” Stallman said.
Unless Microsoft makes an “ironclad commitment that its present and future patents will never be used against implements” of .NET, the open source leader cautioned developers against building applications with it.
“The basic point,” Stallman explained, “is that Microsoft has patents over features in .NET, and its patent promise regarding free software implementations of those is inadequate. It may someday attack the free implementations of these features.”