This is a serious and timely issue (July 2003). The most powerful Linux adversary (Microsoft) stated in their internal memorandum (leaked to the press) that they should try the legal route to deal with Linux ("The discussion of IP rights needs to be tied to concrete actions"). The entertaining (and "scary") Microsoft series of blueprints on how to deal with Linux have been leaked and published as so-called Holoween Documents (http://www.opensource.org/halloween/).
So yes, there is some probability that Linux might be sued out of existence in the United States because of political pressure.
Linux developers are not copiers or thieves. They produce thousands of lines of computer code every day. The Linux licence is based on the respect for the "intellectual property", i.e., the exclusive right of the author to distribute her creation. Nevertheless, misappropriation of code into Linux can happen. Considering the amount and complexity of code in a typical GNU/Linux distribution and the rate of development, it is likely going to happen, sooner or later. A dishonest developer may "lift" code from somebody else and submit it to any of the number of public Linux-related projects, pretending that the code is his own. This IP problem is not limited to Linux. Cases of misappropriation of code happen to close-software companies as well (e.g., it happened to Microsoft) and, no doubt, will happen again.
As far as potential for misappropriation of code is concerned, the major difference between the "open source" and "propriatory, closed software" is that a misappropriation is trivial to detect in the former, and almost impossible in the latter. It the obligation of any IP owner to protect their IP and report potential (involuntary) infringements so it can be promptly remedied, and their potential losses minimized.
Linux developers are not negligent. They continuously submit all the Linux source code for public review and comment so as to detect and prevent any IP violations. Well-organized Linux archives are maintained. The open development method of Linux follows that employed by science, and it is likely a more dilligent practice for protection of other authors' rights than almost any IP control system conceivable for implementation in a closed-software house. Thus, Linux management of IP rights can rightly be called as "among the best in the industry" if not "the best".
Linux has an excellent IP record. Certainly, it is not known to harbor misappropriated code. Is it then legally-safe for me to use Linux? I feel, it is for me. In case a misappropriation of code into Linux is ever found, I can be certain that any infringing code will be immediately expelled from Linux and "clean" version will become available for me to upgrade. It has always been a specific goal of the Linux community at large to produce code uncontaminated with any propriatory code.
The whole issue should be placed into a broader context. There appears to be a recently increasing tendency to go overboard with "intellectual property" which clashes with notions of basic justice, decency and common sense. It seems that some dishonest corporations try to impose nebulous "licensing" to keep extracting, indefinitely, money while delivering no new value. In some cases, IP is becoming a tool with which some major corporations try to tax the average joe (and business startups), not unlike emperors used to tax salt. Linux is an answer to this unhealthy trend, an answer which is based on respect to the existing copyright laws. Therefore, Linux clashes with those who wish to extract money while delivering no value. I do not see a fundamental problem with IP in Linux but there is certainly a conflict of interests and hence attacks on Linux.
To summarize, Linux licence is based on respect to the current copyright laws. For all what is known, Linux is free of "intellectual property" infringement. It employs the best due diligent practices to make sure it remains free of any such infringements. However, due to the revolutionary nature of source code development, Linux is being attacked with nebulous IP claims and smeared by some paid "experts" with various IP "worries". So yes, publicity is expected as Linux big names are dragged through U.S. courts but it does not affect me.
If worst comes to worst and the intellectual property laws became so restrictive as to impede the progress of Linux and other open software, I would expect that it will be the laws that crumble. This is because the politicians seem to forget the intellectual property does not really exist (as Jefferson knew) and have been put in place only for further development and common benefit. Linux was born from genuine frustration about the quality and cost of software produced by the past methods, and such frustration cannot be contained by naked force without political repercussions.[an error occurred while processing this directive]