Hello,
it can take some time to analyze the file especially for Android, for Windows you have many Tools to analyze Files.
Android are out since last year, before there were almost no viruses for Android. See here: http://blog.gdatasoftware.com/blog/article/mobile-malware-the-barrier-of-the-beast-is-broken.html
And not everything comes in the Database when it would give to many False Positives.