If you are still using Internet Explorer 6, you should update your system immediately.
Then schedule your automatic updates for an appropriate time. While not immune to attack Mac viruses are very rare.
At which point they are forced to find a technician (I can't tell you how many times friends have asked me to fix their computers) or ,more likely out of frustration, just go out and buy a new computer.
This costly decision can be avoided most of the time.
They are increasing in popularity but still a very small percentage.
There are several options out there for Mac Virus protection most are yearly subscriptions.