Please bear in mind that a security program that works well on one person's computer may not work well on another person's computer. Each computer is configured differently and has a different range of software programs on it. The amount of memory a computer has, the kinds of programs, what the user likes, the user's experience, and the user's needs all have a bearing on what to use for protection.
A case in point. Many people find Windows Defender an excellent antispyware program. However, in my case, the program causes several problems. Sometimes the program shuts down. In other instances, it causes my computer to shut down, so for me that is not a good security program to have on my computer.
There are many free security programs listed here: http://www.bleepingcomputer.com/forums/topic3616.html