No single product is 100% foolproof
and can prevent, detect and remove all threats at any given time. The security community is in a constant state of change as new infections appear and it takes time for them to be reported, samples collected, analyzed, and tested
by anti-virus researchers before they can add a new threat to database definitions. Further, if you're dealing with zero-day malware
it's unlikely the anti-virus is going to detect anything. Malware writers have the advantage since no matter how hard security vendors attempt to stay on top of new threats, there is always a short time-frame in which a new malicious file goes undetected
and can infect a computer without detection. Just because one anti-virus or anti-malware scanner detected threats that another missed, does not mean its more effective. Every security vendor's lab and program scanning engine is different. Each has its own strengths and weaknesses and they often use a mix of technologies to detect and remove malware.
Keep in mind that no amount of security software
is going to defend against today's sophisticated malware writers for those who do not practice safe computing and stay informed. It has been proven time and again that the user is a more substantial factor in security than the architecture of the operating system or installed protection software. Security begins with personal responsibility
and following Best Practices for Safe Computing
. Knowledge and the ability to use it is the best defensive tool
anyone can have.