How much does unwanted Internet traffic cost an organization?

This is a good older article reflecting the real costs associated with "junk email" from the Internet.  While it's difficult to ascertain costs, there are expenses in handling SPAM and junk email.  I'm suspecting if other costs were factored in (e.g., lost user productivity, help desk calls, spam blocking software, etc), the costs would be significantly more than just the bandwidth costs noted in this research.

How much does unwanted Internet traffic cost an organization?
http://articles.techrepublic.com.com/5100-1009-5967393.html

QUOTE: A few weeks ago, a coworker asked me a simple question: How much of the Internet traffic coming into our network was "junk," and how much was this unwanted traffic costing us?

Statistics:

* Approximately 2.8 million distinct IP addresses from all over the world were responsible for junk traffic on my organization's network in the past month. And keep in mind that this doesn't include delivered junk e-mail.

* Roughly 40,000 networks that were responsible for junk traffic on my organization's network in the past month.

* Statistically, the majority of junk IP addresses came from inside the United States

* Second on the list for junk Internet traffic was China. Rounding out the top five on my list of junk Internet traffic sources were France, Belgium, and Germany

* Approximately 7 percent of all incoming Internet traffic to my organization's network fell under the junk traffic classification.

* Estimating the cost for bandwidth at about $50 per megabit per second, the junk traffic costs my organization about $255 per month—or about $3,060 annually.