According to Android.com, more accurate OS version detection methods, using stats from Google Play visits, shows that most users are noe using Jelly Bean – Yeey. The more phones running the latest version, the more up-to-date/secured Android devices..
As you May notere, users of third party app stores are not included in these numbers. I believe there are unfortunately a lot more old Android versions running than what is reflected by Android.com. However, from a security point of view, I would like to add to the discussion of Android Vs iOS (when it comes to Malware stats) that the Google Play stats of OS versions reflect best what can be compared to Apples Appstore and their numbers of malicious apps.