Actually cats may be more prevalent than porn. Porn maybe ubiquitous but many sites are dying due to people reposting their content on free tube sites. Copyright violation may be the death of the porn industry in it's current incarnation, as porn is moving less towards films and traditional paysites, and more towards independent models who own their own site and whom get paid for cam sessions where you pay to see them doing something or other with someone or other. Porn isn't even the top target for infection with malware now, it's celebrities, online gambling, etc.
