Bugs & viruses

Sorry for the silly question! I have been told that macs are not suspect to viruses...but then people were told the Titanic was unsinkable!
1. Is that true?
2. Do I really need an anti-virus software? I've seen the products advertised, but I don't want to have to spend the money if I don't need to.

I do keep my data backed up.

Thanks for any help on this!

Ok, ok, so I just can't help myself.

Have a read of this thread from last week.

http://www.mac-forums.com/forums/switcher-hangout/184131-virus-question.html

http://www.mac-forums.com/forums/switcher-hangout/23835-official-mac-antivirus-firewall-faq.html

Stickies are helpful.