But new rules for software contracts put out by The American Law Institute have united the enemies as part of a growing protest of tech companies and their lawyers. The most controversial of the guidelines is that software vendors must guarantee buyers that there are no hidden flaws in the software.
Industry lawyers say the rules will create undue product liability for companies and developers because of the inherently flawed nature of software.
"It creates an unrealistic standard and a lot of litigation," said Mark Radcliffe, a DLA Piper lawyer who's worked to oppose the new rules. "Any project that has Microsoft and Linux on the same side, you know there's something wrong."
The Principles of Law of Software Contracts, as they are called, were passed in mid-May by ALI, the venerable and scholarly group that clarifies laws. The principles are not law, but they serve to guide judges, who frequently cite them in decisions, and may be adopted by states.
Robert Hillman, a Cornell Law School professor who headed the multiyear project for guidelines to clarify software contract law, said the criticism that the changes will bring a lot of litigation is overblown.
"That's the cry of anyone who opposes any law -- that it's going to create litigation," he said. "Fraudulent concealment law is as old and established as any law, which is all we're doing here."
The debate divides consumer protection advocates, who say software companies should be liable for the quality of their products, from the industry, which calls the principles unnecessary and potentially crippling.
Hillman said that "users of software are very supportive of this, and for the most part we haven't heard from a lot of the industry."
But both Microsoft and Linux -- Microsoft CEO Steve Ballmer once called Linux a "cancer" and open-source advocates consider Microsoft an evil empire -- joined together to oppose the changes. They submitted an open letter (pdf) of protest before the principles were adopted. "There is no great failure in terms of substandard quality or unmet expectations that would justify imposition of mandatory new rules, particularly given the existing remedies under misrepresentation and consumer protection law," the joint letter stated.
ALI backed down on a couple of proposals that might have especially hurt open-source software developers. They removed a section that would have made companies and developers liable for IP infringement in the software they sold. They also limited the guarantee about hidden flaws to software that's sold (open source is given freely).
But DLA's Radcliffe said that will be a difficult distinction since software is now often given away, with only services, such as technical support, being sold.
He and others also said there is uncertainty about how to interpret the controversial section. The wording of the guarantee is that the software "contains no material hidden defects of which the transferor was aware at the time of the transfer."
"Most lawyers are concerned about what's material, what's known, what's a defect and what's distributing for money," said Heather Meeker, a Greenberg Traurig lawyer who was an adviser on the project. "We know as lawyers we could argue about that until the end of time."
Jane Winn, a professor at University of Washington Law School who also was an adviser on the project, said leaving this type of software product liability up to the court system isn't the right call because of the complexity in figuring out what and who is responsible for software that doesn't work.
"There's no question that the current liability regime is inadequate, but the solution might be agency regulation rather than a common law principle," Winn said.