Obtaining private data from a user's Facebook profile to create an application is usually necessary, say the heads of two app development companies.

The problem, they say, is some of this data gets mined, either through app developer cooperation or not, and then sold to advertisers. A recent report from The Wall St. Journal exposed this problem, saying some third-party applications take a user's private data and subsequently sell it to outside advertisers. This problem is very real according to developers.

Most apps need information from a user's profile to function properly, said Udoka Mark Uzoka, president of Facebook app developer company Social Cubix. If the app gathers this information, some apps can store them, so when the user goes back to the app, it resumes where they started without trouble. It's up to the app owner to respect the privacy of an app user and not use the app to make money with advertisers.

Most of the private data, Uzoka says, is basic information, such as a person's name, gender and age. However, sometimes certain apps require more specific data. For instance, an app that helps a user find information about bars around a college town would need to know where that person went to school.

As an app developer, Uzoka says the problem is essentially out of his company's hands once the project is finished. Since they are independent contractors, what their clients do with the app is completely up to them.

If you turn the app over to an owner and say here's your app, it's yours since you paid us, the owner can then contract another developer to make sudden changes to the code in order to mine data. I could refuse that request to mine data, but they can get someone else to do it for them, Uzoka said. Some people intentionally develop apps that mine and sell data. If there was an immediate way to stop it, Facebook would have stopped it already, Uzoka said.

Brenton Gieser, executive partner at ConvoSpark, a company which also develops apps for Facebook, says there is a built-in incentive to provide more information.

Some of the app developers, I can say with a degree of certainty they are pretty responsible people to a certain extent. There are the big app developers, the Zyngas and Playdoms, they are dealing with different advertisers. The more information and data they provide advertisers, the better they will get in return, Gieser said.

Gieser said he wanted to point out he wasn't accusing Zynga, Playdom or any big app developer of selling private information to advertisers, he just said it would benefit them to do so. Zynga was one of the companies mentioned in the Wall St. Journal report.

Efforts to reach Zynga and Playdom were unsuccessful.

Even though it's not always in their hands, Uzoka says there is something app developers could do to prevent data mining from happening. Developers need to take a stand when there is a request and say we cannot take this information, if the app doesn't need it to work. You need integrity on the part of developers. You contracted me to develop the app and we'll develop as you've contracted, he said.

He adds that developers should try and cut down on the need to store a user's information. If the app developer does need to store the information, there should be a clear cut privacy policy. Most Facebook users when they are accessing apps are not thinking that app is storing information. They are thinking the app is just running by its profile for what it needs. I'm an advocate for real time user of data and not storing it from the user's profile.

Gieser says even though selling users' private data to advertisers is shady business, it's the kind of practice to be expected when people put their information up on the internet. It's the nature of the internet. I understand every time, I sign on a platform or something new, what kind of access they have, I am taking a calculated risk every time, Gieser said.