Ads in mobile apps opens users to risk
A study of over 100,000 applications in Google Play (formerly Android market) has found that more than half contained ad libraries with nearly 300 of which able to grab code from remote servers that could potentially give malware writers and hackers a away into your smart phone or tablet.
The main problem with ad libraries is that users are essentially giving them the same access permissions as the applications themselves, thus allowing them to skirt standard security processes. It turns out that about half the ad libraries could track a user's location via GPS and access phonebook data.