The aim of Microsoft's shared source programme is to allow expert users to improve the performance of their software.
Windows has been designed as a complex system, even by operating system standards. Without access to sufficient code, developers are in danger of solving one problem at the expense of creating others elsewhere.
This is a worry for companies, typified by the comments of Ian Muir from insurer Standard Life's information systems analysis and design division.
While welcoming Microsoft's move to allow access to its source code for developers, Muir said, "We view it as being of more relevance to independent software vendors who supply us with products based on the Microsoft platform.
"By making available the source code we anticipate that these products will see more functionality and quality improvements."
Muir concedes that working inside the operating system can be fraught with dangers. He said, "It is very unlikely that Standard Life bespoke developments targeted at the Microsoft platform would ever have to delve into Microsoft's source code - and it is not something we would encourage."
Dan Kusnetzky, IDC vice-president of system software research, said competent programmers writing complex file system applications or network code may not be so proficient when it comes to operating systems. "Operating system coding requires different skills which may be beyond these people because it is developed according to a different methodology or even in a different programming language.
"Having access to the source code may be no help at all," Kusnetzky said.