Free apps have been around forever. Developers make the app, give it for free, and if people like it they are asked to make a donation. Others use banner ads to make a little cash. Lately though, it seems more common that developers are taking it a step further. Personal information carries a price, and some Android apps have been using personal data in interesting ways.

Researchers used something called TaintDroid, an extension to the Android platform that tracks the flow of sensitive data through third-party applications. It automatically labels (or taints) data from privacy-sensitive sources, and logs the data’s labels, the application responsible for transmitting the data, and the data’s destination.

The study found that 358 apps in the Android Market require Internet permissions, as well as permissions to access location, camera, or audio data. Of those 358, researchers randomly selected 30 apps, including ones for The Weather Channel and BBC News.

TaintDroid flagged 105 instances in which the apps transmitted tainted data; 37 of which researchers said were legitimate. Overall, the report found 68 instances of potential misuse of users’ private information across 20 applications, the report said.

Fifteen of the 30 apps reported user locations to remote advertising servers, and seven apps collected the device ID, and sometimes the phone number and SIM card serial number. One app even transmitted phone information every time the phone booted – even if the app has not been used. Overall, two-thirds of the apps used data suspiciously, researchers concluded.

Not only are these apps transmitting data, but they try to get your information in other ways. This week I tried to download a copy of Lookout Anti-Virus for my Droid. The app forces you to create an account with the company before you can use it. Later I downloaded Caller ID Faker and found that after you key in the phone numbers you wish to use, it forces you to provide an email address before you can make a call. It’s all behavior I don’t trust. I’ve chosen to uninstall these apps. The free price isn’t worth the chance at getting even more spam email than I have now.