Microsoft's recent patent deal with Novell, owner of Suse Linux, came with the implicit threat that if you run another Linux distribution, Microsoft might sue you. CEO Steve Ballmer made it a bit more explicit last week. "Anybody who's got Linux in their data center today sort of has an undisclosed balance sheet liability," he told the Professional Association for SQL Server, in a discussion posted on the Seattle Post-Intelligencer's site.

Why Microsoft's sudden Linux engagement? It's trying to extend its Windows strength into next-generation data centers, which will have virtualization at their center. It must make it easier to run Linux virtual machines under Windows, and vice versa.

But Microsoft is in essence threatening its own customers, who are far more likely to use Red Hat Linux than Suse. Red Hat won't cut a deal. So Microsoft has two choices: It could keep threatening until it actually has to sue someone, or it could make faster progress on delivering its software as a virtual file package and making Windows more practical in a virtual appliance, where the operating system is tuned to work with a particular app. That, not legal saber rattling, would get would-be Linux users' attention.

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