I'm connecting to the internet through a router at the moment, a Linksys WRT54G, do I need to have a software firewall set up? It seems kind of redundant if you're never going to directly connect to the modem.
A software firewall on your computer can be useful because it can alert you to unexpected OUTGOING connections. A hardware firewall (because it has no user interface) pretty much has to let outgoing connections happen by default because otherwise you can't do anything with it! A software firewall can be more discerning - Internet Explorer should certainly be making connections, while a program you've never heard of trying to make outgoing SMTP (e-mail) connections is probably malware trying to send spam.
This can be bad, of course, because you end up with alerts whenever something that's never connected before comes up, but it quites down after a day or so, and then you only get alerts when you install something new, or something goes wrong.
So, a software firewall CAN be a good compliment to a hardware firewall, but it's mostly useful as a detection tool, and to prevent things like bot networks from spreading. Of course, if you have other PCs on the local network (behind the router), a software firewall will also be useful in preventing local attacks.
Software firewalls are good when you want good control of connections to and from your computer. Other than that they are a weak substitute and only offer very minimal security improvements over a stand alone hardware firewall. A software firewall will likely be a good decent substitute for common sense computing. If you are cautious and use your computer wisely(Not downloading and installing random apps from random places) then you really don't need a software firewall. if you are a careless computer user, like the mob, then they are a great tool.
A firewall is still good for the event of somebody else being on your network. I personally believe there is no such thing as too much security.
A software firewall does give you the option to control what going out of your computer onto your local network, so in some cases it can stop the spread of some exploits. Likewise it can stop malware from being spread to your machine from other local boxes.
i have no intention to parttake in a discussion about the pros and cons of software firewalls, but since you have a Linksys WRT54G, why not using DD-WRT, a powerful 3rd party firmware, and setup a decent hardware firewall using iptables.
Note: not all WRT54G are compatible with DD-WRT, look for your version here.
I second [Michael Kohne]
Your router should by default include a firewall, if it does not then assume all ports are always open.
You dont NEED a firewall on your router but it is HIGHLY suggested that EVERY computer has a firewall of its own up and running when connected to this modem. In short your don't NEED a firewall at all but any technician would not recommend you naked through the web.
If you need a firewall for your computer i suggest you use Avast or AVG. (without piracy)
You dont need to be directly connected to the modem to catch a virus, (this seems to be your thinking). If your connected by wire or wifi you can pass viruses.