1- For a complete 1-application solution, I recommend
A-squared AntiMalware 4.0 (A2AM).
A2AM includes Mamutu (behavior-blocker HIPS), plus Ikarus (AntiVirus engine and signatures), plus Anti-HiJack, plus A-squared (second engine & signatures for anti-trojan, anti-spy, anti-worm, anti-keyloggers, anti-dialers, etc.).
2- A good 2-application option is: {a} Malwarebytes AntiMalware (on-demand version -- it's free), plus {b}
Twister AntiVirus (includes antivirus, plus registry protector, plus behavior-blocker HIPS: "Filseclab Dynamic Defense System").
3- Both of the above solutions are "aggressive" -- for high-risk users -- potentially yielding above-average number of False Positives (FPs) during the first couple of full system scans. For fewer FPs, but requiring an additional application to attain protection ~equal to the above two solutions, I recommend...
{a}
Avira AntiVir (free AV covering a broad spectrum of malware, but not strong on antispy coverage), plus {b} Malwarebytes AntiMalware (on-demand version -- it's free -- gives excellent coverage of spyware and other malware types), plus {c}
Threatfire (free behavior-blocker HIPS).
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NOTE 1: To ensure computer stability, it is WISE to never run more than one antivirus in real-time-monitor mode. Also, never run more than one HIPS in real-time-monitor mode. All of the above combinations are almost always stable, given the preceeding caveats.
NOTE 2: It is WISE to always make an image of your system disk (usually c:\) before trying-out ANY major security software. Good imagers include {a}
Drive Backup 9.0 Express (free), and {b}
Image for Windows (not free).