Android is going from strength to strength. Around 600m of the nearly 2 billion smartphones ever sold use Google’s mobile operating system, estimates Horace Dediu, the boss of Asymco, a mobile-analysis firm. How odd, then, that nearly two-fifths of those that remain in active use, both old and new, rely on outdated versions of it.

Glenn Fleishman explains one of the biggest flaws of Android – how cheap handsets, fast development and loose controls by Google adds up to hundreds of millions of handsets running outdated and unpatched versions of Android operating systems.