A debate has opened in the software development community over so-called open source operating systems (and other programs), ones for which the source code is freely released for public analysis. The arguments are predictable: With open source, many critics can peruse the code, presumably finding flaws, whereas closed (proprietary) source makes it more difficult for attackers to find and exploit flaws.
The Linux operating system is the prime example of open source software, although the source of its predecessor Unix was also widely available. The open source idea is catching on: According to a survey by IDG Research, reported in the Washington Post [CHA01], 27 percent of high-end servers now run Linux, as opposed to 41 percent for a Microsoft operating system, and the open source Apache web server outruns Microsoft Internet Information Server by 63 percent to 20 percent.
Lawton [LAW02] lists additional benefits of open source:
Cost: Because the source code is available to the public, if the owner charges a high fee, the public will trade the software unofficially.
Quality: The code can be analyzed by many reviewers who are unrelated to the development effort or the firm that developed the software.
Support: As the public finds flaws, it may also be in the best position to propose the fixes for those flaws.
Extensibility: The public can readily figure how to extend code to meet new needs and can share those extensions with other users.
Opponents of public release argue that giving the attacker knowledge of the design and implementation of a piece of code allows a search for shortcomings and provides a blueprint for their exploitation. Many commercial vendors have opposed open source for years, and Microsoft is currently being quite vocal in its opposition. Craig Mundie, senior vice president of Microsoft, says open source software "puts at risk the continued vitality of the independent software sector" [CHA01]. Microsoft favors a scheme under which it would share source code of some of its products with selected partners, while still retaining intellectual property rights. The Alexis de Tocqueville Institution argues that "terrorists trying to hack or disrupt U.S. computer networks might find it easier if the Federal government attempts to switch to 'open source' as some groups propose," citing threats against air traffic control or surveillance systems [BRO02].
But noted computer security researchers argue that open or closed source is not the real issue to examine. Marcus Ranum, president of Network Flight Recorder, has said, "I don't think making [software] open source contributes to making it better at all. What makes good software is single-minded focus." Eugene Spafford of Purdue University [LAW02] agrees, saying, "What really determines whether it is trustable is quality and care. Was it designed well? Was it built using proper tools? Did the people who built it use discipline and not add a lot of features?" Ross Anderson of Cambridge University [AND02] argues that "there are more pressing security problems for the open source community. The interaction between security and openness is entangled with attempts to use security mechanisms for commercial advantage, to entrench monopolies, to control copyright, and above all to control interoperability."
Anderson presents a statistical model of reliability that shows that after open or closed testing, the two approaches are equivalent in expected failure rate [AND05]. Boulanger [BOU05] comes to a similar conclusion.