As the title suggests, I was wondering where I could find free software good at keeping out hackers and other ne’er-do-wells. Any suggestions?
Well the most known is Zone Alarm, they offer a free version that works pretty good. There is also Sygate which is similar to Zone Alarm. This page lists a couple of more.
Thanks for the timely thread, Mr. K. And the timely response as well, Toddly. I’ve been thinking I should set-up a firewall, but I’ve been to lazy to look in to it. This thread motivated me; I just installed ZoneAlarm (only the freebie version thus far). Its’ only been 10 minutes, but I’m pleased with it so far.
I’ll definitely second ZoneAlarm. It works. It’s free.
Once you’ve installed everything, you can test your PCs vulnerability using Shiels Up.
Agnitum Outpost v1 is also free.
http://www.agnitum.com/download/outpost1.html
I use it because there’s a free plugin for it called BlockPost where you can set up a list of IPs to be completely blocked.
I’ve used the free version of Zone Alarm for a couple of years. I don’t see anything compelling in the paid version so I’ve never bought it.
I use Google Toolbar to block pop-up ads. Spybot Search & Destroy and AdAware are good for checking for spyware/adware. Also, I run Norton Anti-Virus software. Finally, you should make sure to keep all of these program up-to-date (particularly the antivirus and antispyware software).
Except for Norton, all of these programs are free, and there are freeware antivirus programs as well.
I use AntiVir and it works for me.
I put avast! on another machine and it works nicely as well, although the occasional pirate lingo (i.e. “jollyroger” appearing in an auto-update URL) seems very virus-like instead of anti-virus.
Among the best for PCs: FreeBSD, Linux. When used as intended, you’ll be pretty close to immue to viruses, trojans, and spyware, and pretty nicely insulated from hacking exploits as well. 
Among the best for non-PCs: Having them, instead of a PC. Macs are excellent alternatives.