The Malware problem Mac Users have faced with "Mac Defender" is similar but not the same as Windows Users in the past as far as Spyware, Malware, Adware. Its all annoying, and can leave you very uncertain about Website's etc. Mac's get viruses, and Windows gets viruses its reality, especially in the rich multimedia web experience we all expect, but don't want any risk.
Now that is not too much to ask, but some people out there try and profit from that platform that we all manage our lives in. Not to fear though Apple has done everything they can to help, and restore consumer confidence in there product.
Also we as users have to be careful where we go and how we have our browsers configured etc. We all I think have a responsibility to maintain certain things within our own system. Sometimes unfortunately these things happen. It comes with the territory of this world we are in with the web etc.