There are Anti-Virus packages available for the MAC, and there are virus’s out there for the MAC. However as long as the MAC holds such a small market share compared to Windows, Windows will always be the bigger target.
Because of the much larger user base that Windows has it is simple ROI for the virus writers. It costs then X amount of time to create a virus. You can either spend that time writing a Windows virus which could infect 100 million PCs and get you data from 100 million people, or you could spend the same amount of time writing a virus which could infect 2 million MACs and can only get you data from 2 million people. When you take into account that a virus will infect at most 1% of the computers out there that’s 1 million PCs or 20,000 MACs.
As the MAC becomes more and more popular there will be more and more virus’s written for the MAC (as Linux is starting to discover).
There is a big difference between Windows and Mac. Mac is Linux based, which offers good security for each file separately or as group folder with permission system.thats how a virus couldn’t affect a Mac File easily.