This question already has an answer here:
In testing suspicious files for malware, the typical method is to search for known malicious code. This is why zero-day malware attacks can be so dangerous — their malicious code is previously unknown to antivirus software. The ideal solution is to test every file and program in a sandbox before it is used, and this has been tried, but as far as I know, typically unusual processes appear that can be detected by a smart enough mouse. The malware detects that it is being sandboxed, and holds back on its malicious behavior to keep from being discovered.
The question is, can it be possible, and more importantly practical, to build a sandbox that's identical to an actual computer, and then implement in today's operating systems (Windows, OS X, Linux, iOS, Android) a software which which uses it to test everything before it is run, or even better, uses it as the running environment for that file?