virus on a mac

Hello there.I  already read a little bit about trojanfake.av

but here's my question if anyone can help.

Does a mac computer get affected with virus such as 

trojanfake.av

adwar.clkpotato!gen3

trojan.zbot

trojan.bamital.b

they were all found in my system by a tech. I've never known to have virus affect my computer. Any insight would be greatly appreciated.

I have a 2008 dual core Mac Pro tower

running LION with newest update.

thanks for anyone's help in this.

 

Leo