@articleSchryen_2004, title=Effektivität von Lösungsansätzen zur Bekämpfung von Spam, volume=46, number=4, journal=Wirtschaftsinformatik, publisher=Springer, author=Schryen, Guido, year=2004, pages=281–288 

@inproceedingsSchryen_2004, place=Madrid, title=Fighting Spam: Motivating an Account-based Approach, booktitle=Proceedings of the IADIS International Conference WWW/Internet 2004. vol. 2, publisher=IADIS Press, author=Schryen, Guido, editor=Isaias, PedroEditor, year=2004, pages=937–940