exclusive rights (e.g. copyright), in free software the author's copyright is still retained and used, for instance, to enforce copyleft or to hand out permissive-licensed software. Licensed software is in general not in the public domain. Another distinct difference is that an executable program may be in the public domain even if its source code is not made available (making the program not feasibly modifiable), while free software always has the source code available. Post-copyright public domain With the 2000s and the emergence of peer-to-peer sharing networks and sharing in web development, a new copyright-critical generation of developers made the "license-free" public-domain software model visible again, also criticizing the FOSS license ecosystem ("Post Open Source") as stabilizing part of the copyright system. New non-FOSS licenses and waiver texts were developed, notably the Creative Commons "CC0" (2009) and the "Unlicense" (2010), and there was a noticeable rise in the popularity of permissive software licenses. Also, the growing problem of orphaned software and digital obsolescence of software raised awareness of the relevance of again passing software into the public domain for better preservation of the digital heritage, unrestricted by copyright and digital rights management. Around 2004, there was debate on whether public-domain software could be considered part of the FOSS ecosystem, as argued by lawyer Lawrence Rosen in the essay "Why the public domain isn't a license", a position that faced opposition by Daniel J. Bernstein and others. In 2012, the status was finally resolved when Rosen changed his mind and accepted the CC0 as an open-source license, while admitting that, contrary to previous claims, copyright could be waived, as backed by a Ninth Circuit decision. Passing of software into the public domain Release without copyright notice Before the Berne Convention Implementation Act of 1988 (and the earlier Copyright Act of 1976, which went into effect in 1978) works could be easily given into the public domain by releasing them without an explicit copyright notice and no copyright registration. After 1988, all works were by default copyright protected and needed to be actively given into the public domain by a waiver statement. Leaving the copyright term Copyrighted works, like software, are meant to pass into the public domain after the copyright term, losing their copyright privilege. Due to the decades-long copyright protection granted by the Berne Convention, no software has ever passed into the public domain by leaving copyright terms. The question