    @article {Zhou2007,
	title = {An Effective Multi-layered Defense Framework Against Spam},
	journal = {Information Security Technical Report},
	volume = {12},
	number = {3},
	year = {2007},
	pages = {179-185},
	publisher = {Elsevier},
	abstract = {<p>Spam is a big problem for email users. The battle between spamming and anti-spamming technologies has been going on for many years. Though many advanced anti-spamming technologies are progressing significantly, spam is still able to bombard many email users. The problem worsens when some anti-spamming methods unintentionally filtered legitimate emails instead! In this paper, we first review existing anti-spam technologies, then propose a layered defense framework using a combination of anti-spamming methods. Under this framework, the server-level defense is targeted for common spam while the client-level defense further filters specific spam for individual users. This layered structure improves on filtering accuracy and yet reduces the number of false positives. A sub-system using our pre-challenge method is implemented as an add-on in Microsoft Outlook 2002. In addition, we extend our client-based pre-challenge method to a domain-based solution thus further reducing the individual email users{\textquoteright} overheads.</p>
},
	keywords = {Network Security, Security service, Spam},
	issn = {1363-4127},
	doi = {10.1016/j.istr.2007.05.007},
	url = {http://www.sciencedirect.com/science/article/B6VJC-4NS2GR9-1/2/d542b6d1b936f796cad17284a6edbc69},
	author = {Jianying Zhou and Wee-Yung Chin and Rodrigo Roman and Javier Lopez}
}
