coopster - 11:53 pm on Mar 17, 2007 (gmt 0)

Are you referring to section 5 in regards to the hyphens?

5 Qualitative aspects of spam hosts Finally, we wanted to evaluate the prevalence of different spamming aspects. For this end, and as a preliminary study, we ran a second round of evaluations by sampling at random 200 hosts that were tagged by at least two judges as Web spam. We wanted to examine the most relevant features found in hosts that were tagged as spam. After inspection of these hosts, we decided to tabulate them using the following (non-exclusive) criteria: Keywords in URL: The host contains keywords in the URLs, separated by minus, underscore or the plus sign. This is not necessarily a spamming aspect. . . .

I think they have just discovered a "qualitative aspect" of many hosts then, spam host or not. I do note that they discount this as "not necessarily a spamming aspect" though.