If you've used ad-sponsored Android apps, you've probably wondered where those ads are coming from, and whether or not there's anything to be worried about. According to French researchers, you have a reason to be cautious. They've found a way to automatically scan Android apps for connections to advertising and user tracking sites, and some of those programs are more than a little dodgy. A selection of 2,000 free Google Play apps connected to a whopping 250,000 sites spread over 2,000 domains. Most of them talk to only a handful of sites (Google's ad services dominate the top 10), but 10 percent connect to 500 or more -- one egregious offender links to over 2,000 sites. Only 30 percent of the apps talked to user tracking sites, but some of those were communicating with 800 or more addresses.