shows users what types of personal information other apps may collect, drawing on an analysis of more than 65,000 popular iOS apps.

BitDefender found that 41.4 percent of apps tracked users' locations, and nearly 20 percent accessed users' address books, in some cases . Clueful checks the user's list of installed apps against the analysis.

But after an initial approval and launch in May, Apple removed Clueful from the App Store. In a , BitDefender said it's still studying Apple's reasons, and didn't offer any other explanation. The company has not responded to a request for comment from PCWorld.

The problem may be that Clueful doesn't monitor users' apps directly, and instead relies on a separate analysis of the App Store. As , Apple's review guidelines prohibit "incorrect diagnostic or other inaccurate device data." By drawing on an external study of only popular apps, Clueful's warnings may be prone to inaccuracy or omissions.

Still, Clueful's workaround may be the only method available on iOS, where apps can't simply look up the permissions of other installed apps. On Android devices, apps such as and the premium version of perform a direct analysis on the users' app library. Neither service is available on iOS. (Lookout offers an iOS app, but without its so-called "Privacy Advisor" feature.)