Seasoned open source code developers are concerned that an effort to produce an open source alternative to Microsoft's .Net development platform may be held hostage by the software giant, if the endeavour ever gets off the ground. Open source critics of Microsoft said the company would have the opportunity to strangle an open source project by demanding a licensing fee and royalty payments each time an open source version of its patent was implemented. They fear developers will flock to the new initiative, code-named Project Mono, only to find themselves trapped in payments to Microsoft later. A requirement for a volunteer developer group to pay licence fees or royalties would be enough to end many open source projects, its advocates said. The .Net set of technologies, due late this year, interests developers because it offers to let a variety of languages work together in building Internet applications. But some say pieces of .Net could contain Microsoft patents. One patent is believed to underlie Windows' file transfer protocol, which will probably be used in .Net. The patent covers only the encryption procedures for how a user password is changed, but as part of the transfer protocol, it is a potential dependency for all developers who have to mimic the Windows file system and seek to interoperate with it. For example, successful interoperation with Samba might make the Samba project subject to Microsoft demands for patent licences and royalties. "The real danger is that there are hidden patents [on .Net technologies]", said Eric Allman, chief technology officer of Sendmail and the original author of the dominant message transfer agent software on the Internet. Developers who use .Net may be subject at any time to demands for royalties. A patent owner that declines to issue a licence may also go to court and ask for an injunction against the further use of its technology, said Tim Cahn, an attorney of Legal Strategies Group, an Internet law firm in California. Jeremy Allison, a lead developer of Samba file sharing between Linux and Windows systems, said keeping an open source project in step with Microsoft's changes to its architecture "is a constant treadmill. If they think Microsoft is going to play fair, they're insane." Project Mono is the effort of Miguel de Icaza, a noted Linux user interface developer and CTO of Ximian, a Linux desktop applications company. "If I were Miguel, I might find myself surprised by hidden patents in .Net," warned Brian Behlendorf, lead developer of the Apache Web server, one of open source code's biggest success stories. Microsoft at press time declined to confirm the existence of the patent. Jan van den Beld, secretary general of ECMA, the European body where .Net specifications are being fashioned into an international standard, said Microsoft does not have to disclose any patents on .Net technologies, unless it is not willing to license them in a nondiscriminatory fashion. Most parties with patents are not required to disclose them in the standards setting process, van den Beld said. When Craig Mundie, Microsoft's senior vice president of advanced strategies, was questioned on the patent issue before the O'Reilly Open Source Conference in San Diego 26 July, he said only that Microsoft would abide by the rules and procedures of ECMA on any patents that apply to .Net. Allison said he inadvertently learned of a patent from "a high Microsoft official" with whom he dined several months ago. He said as they discussed the Server Message Block's password changing scheme, the Microsoft representative, whom he declined to identify, commented: "You know, we have a patent on this, don't you?" De Icaza said last week he is moving ahead with his Mono Project. He has hired an attorney to investigate which patent rights exist in connection with .Net, and plans to implement .Net technologies with technologies already in the public arena - and not subject to claims of patent protection. See the Developer News Section for jobs and the latest headlines. Have your say on all developer topics. From j2ee, to C++, from Visual Basic to Javascript plus much more. Share your experience with others on the Developers Forum Let the editors know what you think in the Mailroom. And read other letters.