Depends on what “simple and free” mean. Not requiring any thought or effort, disallowing any frustration or dollar cost, and imposing no learning curve? Can’t be done.
I tell them to keep the system fully patched. They won’t.
A few months ago I used to install NOD32 and Comodo firewall and tell them to use Firefox with NoScript. I tell them exactly how to use it. These are brute easy to use, though only when everything is working.
For totally zero price AVG is the best. Install AVG Anti-Rootkit Free, Anti-Virus Free, and Anti-Spyware Free. Install the Comodo firewall and Firefox with NoScript as above.
Those people WILL open phishing urls.
The AVG Anti-Spyware Free is a development from Ewido, and is probably the best spyware-trojan freeware available. Occasionally SpyBot (the TeaTimer function works well, but can drive the impatient and learning challenged crazy) or Ad-Aware find something that NOD misses.
If you are working through an unsecured WiFi connection do not use a normal browser but instead use Torpark. Torpark puts in a cryptologically secure link to an anonymising server and is secure enough if the file sharing and WiFi hookup are set correctly and one is running a low level password.
I thought that Windows Defender and Spybot gave some real-time protection, and that zonealarm was pretty unbeatable for a free firewall.