No you don't because linux doesn't get viruses and spyware :)! Thats why i love it!!!

if you really want to install some antiviurs and firewalls, try ClamAV for antiviurs and Firestarter for a firewall. They are both in the repos (the add/remove button for you ubuntu users :P) or you can just type this in the terminal: sudo apt-get install -f clamav firestarter and install any dependencies it needs too :P the only real use I see for the antivirus is to scan files that may already have a virus attached that you may send to a windoze user :P otherwise, the last virus that I heard of one Linux was several years ago (and it was only a proof of concept and didnt do any damage, plus now the kernel is a lot more secure)

There is no real need to do that.

I've used Linux full time for the last several years, and have never had any problems with viruses (though you can install ClamAV if it gives you peace of mind). The Unix/Linux model has the user operating in "normal" level (as opposed to administrator/root level) by default, and this prevents the unauthorized installation of malware (and very little malware exists for Linux). Added to that are the frequent updates to the operating system and its applications, the availability of applications through trusted repositories, and the lack of piracy, and your chances of harm go down even further. Ubuntu is designed as a desktop Linux, and comes with all of its "ports" closed by default, so unless you need to open one for a specific application, you're safe there, too. I have a firewall built in to my router, but if you connect directly to the Internet, you might check out "Lokkit". It's extremely simple to set up; you don't even really need to understand much about what a firewall is in order to get it working. "Guarddog" is another good choice, but is more complex. Welcome to Linux! Visit the Ubuntu forums whenever you need serious help, and you're guaranteed to find an answer.