The US Patent Office has upheld Microsoft's claim of patent rights over its File Allocation Table.

The decision reverses two earlier judgements and potentially allows Microsoft to go after open-source developers who use the technology. FAT controls how computers store information to hard drives and other storage devices such as Flash cards.

The US Patent and Trademark Office ruled that the file system is "novel and non-obvious" and, therefore, deserving of a patent.

The decision is important because it could mean Microsoft could force open-source distributors to pay it a royalty or remove the software from their products. Open-source software must, by definition, be patent-free. Concerns over patents within some Linux distributions have been blamed for hindering wider adoption of the operating system.

Florian Mueller, founder of nosoftwarepatents.com, said the decision gave Microsoft the weapons to attack Linux. Mueller said: "This is now a situation in which Microsoft could cause major problems to Linux vendors and users. Microsoft may not want to do that yet for other considerations, but the USPTO's decision gives Microsoft the strategic option to do so at a time of its choosing. Also, the USPTO and even the European Patent Office continue to grant new patents to Microsoft daily, and some of them may be equally dangerous to open source as the FAT patents.

"The example of the FAT patents shows that all those patent quality initiatives and patent pledges have no significant value to open-source developers, vendors and users if Microsoft ever wants to go for Linux's throat."

Microsoft was unavailable for comment.®

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