The US Court of Appeal for the Federal Circuit has rules that violation of an open source licence can indeed be deemed copyright infringement.
Strong open source licenses such as those drawn up by the Free Software Foundation are used by authors, typically of computer software, who want to make their work publicly available in a way that prevents it being “privatised” by incorporation into a “closed” proprietary system. Examples include the Firefox web browser program that you may use to access this, and the Apache web server program that very likely delivered the web page to Firefox.
The case Jacobsen vs Katzer involved the modification and inclusion of Jacobsen’s open-source computer program (for controlling model trains) by Katzer’s company, which sells such programs for profit.
The Court decided that a copyright holder who dedicates a work to free public use can enforce an open source copyright license to control the future distribution and modification of that work. NUJ copyright activist Mike Holderness comments: “ill-informed advocates of open source sometimes claim that it is ‘anti-copyright’; but if anyone wants to give something away so that it stays given, and cannot be privatised, they need strong copyright and authors’ rights just as much as do authors who want to make a living from their work.”
Read the decision: www.cafc.uscourts.gov/opinions/08-1001.pdf