The evaluation of the 2.4 and 2.6 versions of the kernel was carried out on behalf of Open Source Risk Management (OSRM). (For more on kernels, see below.)
The OSRM survey also found that about a third of the 283 issued patents are owned by large corporations, such as IBM, Novell and Red Hat, that are friendly to Linux.
Twenty-seven of the infringing patents, however, belong to Microsoft, widely perceived as an opponent of free and open source software.
Summarising the position, the report's author, patent attorney and director of the Public Patent Foundation, Dan Ravicher, said: "Bottom line, we confirmed what the community already knew; that Linux, like any other wildly successful product, has a patent risk."
However, he added:
"This patent risk is in line with what we expected to find, and likely comparable to the level of risk you would find in comparable proprietary software; the only difference with open source software being that proprietary software vendors typically provide legal backing for their customers".
As a result OSRM is extending its insurance services to offer a patent insurance program for enterprise Linux users. This follows the firm's introduction of legal protection against copyright litigation for certain versions of the Linux kernel in May this year.
Neither the firm, nor Ravicher would give details as to which patents were identified in the evaluation. According to Daniel Egger, chairman and founder of OSRM:
"Current US patent law creates an environment in which vendors and developers are generally advised by their lawyers not to examine other people's software patents, because doing so creates the risk of triple damages for 'wilful' infringement".
OSRM does not therefore want to put its target market at risk by publishing the patents.
What is a kernel?
A kernel is the fundamental part of an operating system. It is a piece of software responsible for, for example, interfacing with the computer hardware. It can be contrasted with the shell, which interacts with user commands.
The word Linux strictly refers to the Linux kernel, but is also used to describe the entire operating system, also called GNU/Linux, that is formed by combining the Linux kernel with the GNU (pronounced guh-NOO) libraries and tools.
The Linux kernel was originally written by Linus Torvalds and released in 1991. Back in 1983, Richard Stallman had already announced his GNU project, to develop a free operating system. His project progressed, but lacked a kernel, which is how the link with Torvalds' project was formed.