What are the key reasons for or against using open source systems?

Chief Electoral Officer  

Ministry ofEconomic Affairs and the Interior

Statistics Denmark (that run the results processing for parliamentary elections, European Parliamentary elections and referendums on behalf of the Ministry of Economic Affairs and the Interior) have, upon request from a research team at the IT-University in Copenhagen, recently agreed to disclose the code and architecture of their system and have stated that anyone who wants access to this information can have it upon request. While not open source per se, it shows that the Danish authorities are willing to disclose information on some crucial electoral infrastructure for the sake of openness and public trust.