firewalls, anti-virus and spyware

<p>I've just started using Linux a couple of days ago when my windowsXP restore disk for my laptop wouldn't work, so I decided to try Ubuntu instead. So far I'm really enjoying using it. I liked it so much that this morning I created a 2nd partition on my desktop PC and installed Ubuntu to that as well.</p> <p>I would like to ask about firewalls, anti-virus and spyware. Well basically do I need a firewall and anti-virus and what sort of risk is spyware to Linux systems?</p>