iMac Spyware Advice

Hello again

My father has an iMac and sees all the ads about spyware etc, my question is

"Is there any spyware/malware that affects Mac products"

The machine uses a Norton Mac Firewall and Norton AV, and either IE or Nestscape browsers.

Is there anything else needed for this machine either to defeat any spyware or to clean up the machine, not being a Mac user I struggle with this machine

Thank you

Marcus