Some recent anti-copyright infringement laws such as the notorious Digital Millenium Copyright Act (or “DMCA” for short.) or the more recent ACTA, can be used to prohibit the distribution of some open source software, such as those that can be used to break the copyright-protection measures of some content providers.
The Electronic Frontier Foundation has published a document titled “Unintended Consequences: Twelve Years under the DMCA”, which contains a list of “cases where the anti-circumvention provisions of the DMCA have been invoked not against pirates, but against consumers, scientists, and legitimate competitors”.