Time was that SQL Server was the only product Microsoft restricted in this way, and there it could truthfully argue it was only following the lead of Oracle and other competitors it the database arena. But a look at its latest Purchase Use Rights agreement, which governs license rights for all volume license customers, shows the list of such products has grown considerably.

According to the agreement, you “may not without Microsoft’s prior written approval disclose to any third party the results of any benchmark test,” of Microsoft server software, related client software or the .NET framework. This restriction applies to all or parts of Application Center, BizTalk, BizTalk Adapter for MQSeries, BizTalk Accelerator for Financial Services, BizTalk Accelerator for HIPAA, BizTalk Accelerator for Suppliers, BizTalk Accelerator for RosettaNet, BizTalk Adapter for SAP, BizTalk Server 2002 Developer Edition, BizTalk Server 2004 Developer Edition, Commerce Server, Commerce Server 2002 Developer Edition, Content Management Server, Exchange Server 2003, HIS, Identity Integration Server, ISA, Message Queue Service, Microsoft Developer Network Subscription (MSDN), Microsoft Office XP Developer 2002 (MOD), Mobile Information Server, Project Server, SQL Server, SQL Server 2000 Developer Edition, Transaction Server, Visual FoxPro7.0 and 8.0, Visual SourceSafe 6.0, Visual Studio.NET 2002 and 2003 (Enterprise Architect, Enterprise Developer, Professional), Visual Studio Tools for the Microsoft Office System, Web Enhancements Software Development Kit, Windows Server 2003, Windows Server 2003 for Small Business Server, Windows Small Business Server 2003, and Windows Small Business Server, Premium Edition.

Note that Microsoft’s censorship clause doesn’t just say you can’t publish benchmarks – it says you can’t disclose them at all, presumably to anyone, without written permission from Redmond. That leads to all sorts of interesting hypothetical questions. Suppose, for example, your boss asks you to run some performance tests on Exchange Server 2003 to see if your company should deploy it. Can you disclose the results to her without bringing Microsoft police knocking at your door?

OK, I’m being somewhat facetious there. In point of fact, these censorship clauses would almost surely prove unenforceable in a court of law. But we’ve seen any number of examples of how they nonetheless have a chilling effect on public discourse about technology products, such as the episode when Microsoft could not be bothered to give a U.S. Air Force researcher permission to publish Visual C++ benchmark results. The more products Microsoft attaches this language to, the more you have to wonder: what have they got to hide?