Firewalls and anti spyware should be used .. realize that anyone can get access to your computer and Macs are vunerable to snoopers like any computers. As for viruses. I have yet to hear of a good argument for putting anti virus software in a mac. ...... but tomorrow, it may well be necessary
Do a google search for mac virus ... You won't find many hits
imho
G3 OSX10.3.9