What are the security differences between connecting your home computer directly to a broadband modem and going through a router?
Most modern routers come with something called Network address translation (NAT). This means that the 1 IP address that you expose to the internet is translated into the multiple IP addresses required for the PCs within your network. With NAT random incoming packets are not forwarded on to your PC, so if someone tries scanning your IP address and ports, all they will get back is rejection messages from your router (or in some cases, just nothing at all)
It's not by any means foolproof or perfect security, and I would still recommend a firewall on your PC, but having a NAT router between you and your modem is certainly a step up in security.
As a simple demonstration you can try this:
1) Find a firewall that logs blocked incoming connection attempts.
2) Connect your PC directly to the modem.
3) Watch the firewall logs start clocking up blocked connections.
4) Disconnect and attach a NAT router in between.
5) Again, watch the firewall logs and you'll see no blocked connections because the NAT router is blocking them all before they hit the PC.
- Routers generally have firewalls built in that respond to fewer ports than a computer does.
- Routers generally have fewer potential vulnerabilities to the internet than a a computer does. If a vulnerability on your PC is discovered, the router still provides some protection until you get your patch or update applied.
- If a router gets compromised, it is still hard for the "bad guy" to get at the computer and alter/steal/destroy the data on it.
Note that a firewall/router isn't a sure-fire security fix-all, but it protects you from a lot of the low-hanging-fruit seekers.