Truth is that unlike other items, there is absolutely no standards (other than there not being an existing patent) when it comes to software.
In theory, I could copy a piece of code from the Internet that displays "Hello World" and get a patent on it (assuming somebody else hasn't done that yet).
Is it possible that the Linux kernel could have infringements? Possibly. Even antiRepublicrat mentioned that his clean-room program could very well be violating at least one patent--so it's a possibility.
OTOH Iggle, what has MS come up with that's actually innovative besides Microsoft Bob and Clippy?
According to the patent office alone it's 5,000+ things as another poster mentioned. If you feel you can invalidate those claims I suggest you get started.