Sometimes it is possible to patent a technique that is not new precisely because it is obvious--so obvious that no one would have published a paper about it.
For example, computer companies distributing the free X Window System developed by MIT are now being threatened with lawsuits by AT&T over patent number 4,555,775, covering the use of "backing store" in a window system that lets multiple programs have windows. Backing store means that the contents of a window that is temporarily partly hidden are saved in off-screen memory, so they can be restored quickly if the obscuring window disappears.
Early window systems were developed on computers that could not run two programs at once. These computers had small memories, so saving window contents was obviously a waste of scarce memory space. Later, larger multiprocessing computers led to the use of backing store, and to permitting each program to have its own windows. The combination was inevitable.
The technique of backing store was used at MIT in the Lisp Machine System before AT&T applied for a patent. (By coincidence, the Lisp Machine also supported multiprocessing.) The Lisp Machine developers published nothing about backing store at the time, considering it too obvious. It was mentioned when a programmers' manual explained how to turn it on and off.
But this manual was published one week after the AT&T patent application--too late to count as prior art to defeat the patent. So the AT&T patent may stand, and MIT may be forbidden to continue using a method that MIT used before AT&T.
The result is that the dozens of companies and hundreds of thousands of users who accepted the software from MIT on the understanding that it was free are now faced with possible lawsuits. (They are also being threatened with Cadtrak's exclusive-or patent.) The X Window System project was intended to develop a window system that all developers could use freely. This public service goal seems to have been thwarted by patents.