It is being reported that fake Snow Leopard sites are spreading the OSX_JAHLAV.K Trojan. This Trojan has been evolving and performing different levels of havoc, the current manifestation is changing DNS entries which redirect users to malicious sites. From here users may experience phishing and be directed to download FAKEAV which is malicious anti-virus software.
Users should not expect to download free copies of OSX or any software for that matter that is a commercial product. Many cracked software has malicious code and should not be trusted. If you suspect that you may have been infected users should review http://www.magmatic.com/currents/2009/6/23/trojan-jahkav-c-more-to-come.html including the follow-up postings.