Computer Security:
From G4tv.com (Abridged)

Keeping your computer safe is not limited to the internet. You also need to keep it secure when you are not on the internet. Opening files of dubious origin always involves risk of infection or hijacking, but you never know about the ones that your friend brings . Often it's someone else using your computer that infects it unwittingly. Peer to Peer file sharing is also a major source of infection. While in the past most viruses targeted security holes in Windows or Internet Explorer; now most take advantage of social engineering to lure you to click to install something or exploit holes in third party applications like java, flash, acrobat reader, winzip etc. These "zero day" exploits can allow a malicious site to install software silently without your antivirus being able to detect or block them. Keep up to date.

Internet Security: Keeping your computer secure is your first line of defence against hackers, viruses, trojans,hijackers, spammers, and adware. These programs and sites will help you make the a little bit easier. They will also educate you about the threat and your computer, and is one of the most important parts of computer maintenance you can do.

Free Protection:

My favorite; AVG Anti-Virus Free Edition 9.0
Avast Home Edition free for home use
Configuration Tutorial for Avast
A Squared anti-trojan
Comodo BOClean Anti-Malware 4.27
DR Web anti-virus link checker A FireFox Add-on
Google pack includes Spyware Doctor
One of my Personal Favorites; LavaSoft Ad Aware
I love this one; Spybot Search and Destroy
Spywareblaster
Spywareguard Immunize against malware sites.
Super Antispyware

Almost forgot! One of my favorite pieces of Free software; Zone Alarm Free Firewall I've been using it for years.

Adobe Product security vulnerability

Risk Assessment; Low

Adobe Product security Incident response team has posted that a newly discovered vulnerability affecting Adobe Reader and Adobe Acrobat 9.2 and earlier versions. When exploited, this vulnerability could allow a remote attacker to crash the system and execute remote code exploits and take complete control of the affected system. A zero-day attack is already exploiting this vulnerability and is known to download files of a remote server encrypt files and upload them to another site. At the moment this seems to be specifically targeted and the number of infections seen the wild are low.

Adobe has released an advisory on this vulnerability and indicates that a fix will be made available for the affected software on January 12, 2010. As of now, we recommend that users disable JavaScript functionality within Acrobat / Reader from Edit -> Preferences -> JavaScript Category and Uncheck the option "Enable Acrobat JavaScript" and click "OK".

McAfee labs has classified this malware as Exploit-PDF.ag and further information is available from the vil page (see below).

Security Advisory for Adobe Reader and Acrobat
McAfee Vil page, Support, Exploit-PDF.ag

Another freebie I didn't see listed is something I stumbled upon, to my surprise!
MICROSOFT SECURITY ESSENTIALS, a no nonsense application for anti-virus and spyware. It can be found in the Windows Marketplace.