In all my years of using the internet at home, where we are still limited to using dialup connections because of our location, I had never realised quite how important firewalls are for computers which aren't continuously connected to the internet. I used to think the main use for firewalls was to protect those computers which were always connected to the internet and therefore always vulnerable to hacking.
My thinking on that has changed considerably in the past few days having set up a new computer at home for my family. I realised that within minutes of connecting it up, there were machines probing the computer from all around the world trying to find ports on the computer which were vulnerable to attack. Presumably these attempts weren't hackers themselves but drone machines which had become infected by viruses, instructed to probe other computers and propogate the virus wherever they can.
The new computer comes with software which records the details of all attempts to gain access to the computer, which the old machine didn't have. Not having this facility in the past, I've never realised quite how vulnerable machines are, even when they're assigned a dynamic IP address. I had been thinking about it from the wrong angle though, thinking the main threat was hackers knowing who you are and trying to access your data. I hadn't really considered the other side of it, where it doesn't matter who you are as long as your computer is susceptible to being breached in order to install viruses.
I was shocked to find other computers using our ISP, probing for holes in the firewall. Having said that, IP addresses are probably scanned in sequence so computers on the same network will almost certainly be probed before those that are further away, on different networks. Later on in the day I discovered there were upwards of 10 computers a minute trying to access a certain port, many of which were from university residences in the US where viruses are rife. It seemed though that by disconnecting and reconnecting - to obtain a different IP address - these threats went away, at least for now.
It just goes to show how important firewalls are, for any connection. No matter how long or how often you are connected to the internet, you are always at risk of being hacked.