...to follow up on the post above, F-Secure (a third-party who is neither Google nor Apple) reported last month that Android malware grew from 79% of all mobile malware in 2012 to 97% in 2013.
They go on to say that only 5% of these were detected in the US - the third world (especially Saudia Arabia and India) were the major locations of malware detections. Nevertheless, 5% of 804 Android malware threats were identified in the US...which comes out to around 40 of the total.
But these folks also wanted to know what fraction of Android apps were malware, so they also looked at a sampling from various Android app stores, and found malware rates of up to 33%; four non-Google play stores in China were in the top ten, although their rates were below 10%.
In contrast, they found only 0.1% of US Google Play apps to be malware. That sounds like a pretty safe "walled garden", until you realize that Google claims to have 1 million apps in that store, which would thus presumably include around 1000 malware apps. Google says there were >25 billion apps downloaded from the Play store last year; 0.1% of that would exceed 25 million.
0.1% (from the F-Secure study) is also around 100 times higher than the malware rate Google claims (0.001%) in the article linked to above. Both are low numbers, until you multiply them times the number of users/downloads, or until your own phone gets infected.
By the way- the total number of 2013 malware threats from iOS and Windows Mobile combined in the F-Secure study was...
well, y0u kn0w.