It has to be who we give our email addresses to. It's probably innocent. The good people here who complain of pornogrpahic spam, have obviously given their email addresses to some entity that then gave it (more likely sold it) to spammers.
Yep, my first porn started landing in my inbox right after I joined a Yahoo! group several years ago. I think Yahoo! must've given its members' email addys at that time to a third party.