As has been covered in the Firewall section it is very important to protect an computer using the internet with a firewall. Like Anti-virus software there is plenty of choice when it comes to firewall software but there is also the option there for those whop are reluctant to pay or want something free to actually get a free firewall.

Free firewall software is available and is very good. One of the best free firewall software is ZoneAlarm provided free from ZoneLabs.
ZoneAlarm is free for individual and not-for-profit charitable entity use (excluding governmental entities and educational institutions).

The free firewall from ZoneAlarm systematically identifies hackers and blocks access attempts and automatically makes your computer invisible to anyone on the Internet. What this means is that as your computer is made invisible it is harder for a potential hacker to find your computer and if they did then they would then have access blocked.

Another free firewall to look at is Outpost Firewall by Agnitum.

It must be noted that the free firewalls on offer will and do not offer you the same support that you get from a paid version. They are designed for personal use. If you are a company or require that extra support you should look at getting a paid for subscription for a firewall. The free versions will also usually offer paid for versions where you will receive more features and more support!