AirPush serves the most in-app ads to free Android apps, according to research by Juniper Networks. 4.1 per cent of them. Leadbolt was second, serving 2.3 per cent, with Millennial Media (1.5 per cent), AdMob (0.75 per cent) and AdWhirl (0.32 per cent) filling out the top five.

The findings came in a report on free Android apps, with a focus on related security issues. Junipers Mobile Threat Centre analysed more than 1.7m apps on the Google Play store between March 2011 and September 2012. It found that 24.1 per cent of free apps have permission to track user location, while just six per cent of paid apps have this ability.

6.7 per cent of free apps have permission to access user address books, 2.6 per cent can silently send text messages, 6.4 per cent have permission to initiate calls in the background and 5.5 per cent are allowed to access the device camera.

The report highlighted several app categories that were ‘overstepping the needs of the applications when accessing certain permissions’. 94 per cent of free casino and card game apps that have permission to make outbound calls do not describe why the app needs this function. 83.9 per cent that can access the camera and 84.51 per cent that are allowed to send SMS messages do not justify this.

Racing games were found to be the most concerning category with an abnormally high number of apps removed over the time period of the analysis. 99 per cent of paid apps and 92.4 per cent of free apps in this category that have permission to send SMS messages do not explain why they need it. 50 per cent of free apps that have permission to use the camera do so without any description of how or why this capability is being used and 94.5 per cent with the ability of initiating outgoing calls similarly to not describe why.