This last name was originally a typical Scandinavian Patronymic: http://wiki.geni.com/index.php/Patronymics It was only introduced as a last name or family name around 1850-1900.
Hansen is a Danish-Norwegian patronymic surname, literally meaning son of Hans. It is the third most common surname in Denmark, shared by about 4.3% of the population. Hansen is the single most common surname in Norway, not counting spelling variations such as Hanssen, which are also quite common. In the Faroe Islands Hansen is the second most common surname, while in the North German federal states of Schleswig-Holstein and Hamburg Hansen is the third and fifth most common surname, respectively. In Sweden the parallel form is Hansson. The frequent occurrences of Hansen as a surname outside Denmark, Norway and Schleswig-Holstein is due to immigration, though immigrants to English-speaking countries often changed the spelling to Hanson in order to accommodate English orthographic rules.