The lawsuit Microsoft filed against Motorola and its use of Google's Android phone software is awfully familiar.

Microsoft used the same tactic against Linux when the open-source software reached critical mass in the data center and threatened to derail the growth of Microsoft's server business seven years ago.

After name-calling failed to slow Linux, Microsoft started warning big companies that the free software wasn't really free. It also said companies should take into account the potential cost of patent and licensing litigation around open-source products.

Uncertainty increased in 2003, when SCO, a Utah company, alleged that Linux was using some of its technologies. SCO licensed its technology to Microsoft and sought royalties from hundreds of companies using Linux.

That helped Microsoft persuade customers that free software isn't really free. It even promised to indemnify customers that went with Microsoft products instead, offering a sort of insurance against patent issues.

In recent months Microsoft began dropping similar hints about the true cost of Android, leading up to today's lawsuit. It names Motorola, but an accompanying blog post suggests its looking broadly at Android patent issues:

"Our action today merely seeks to ensure respect for our intellectual property rights infringed by Android devices; and judging by the recent actions by Apple and Oracle, we are not alone in this respect," Horacio Gutierrez, deputy general counsel, wrote.

This probably won't have any effect on people using Android phones today or considering some of the new models coming out soon.

The message is for phone manufacturers. Microsoft is telling them that although Google made Android open-source software, it's not completely free, when you factor in the potential licensing costs that may have be paid to patent holders.

I wonder if Google will step up to defend Android, or resurrect the coalition of phone companies that initially backed the software to either fight Microsoft's lawsuit or sort out a licensing arrangement.

Meanwhile, Microsoft is happy to sell the phone companies its new phone operating system, which has presumably gone through a gauntlet of patent lawyers. Apparently Motorola hasn't signed up yet for Windows Phone 7.