Apple last week was sued in San Jose, Calif., for alleged privacy and state business law violations arising from its disclosure of iPhone device identifiers and personal information.

Plaintiff Anthony Chiu, a resident of Alameda, Calif., claims that Apple knowingly transmits data to third parties that can be used to identify users of Apple's mobile devices, without user consent and in violation of various laws. The legal filing also targets 50 unnamed "John Doe" defendants, raising the possibility that third-party developers of apps that use the data in question could wind up in court.

The case hinges on Apple's use Unique Device Identifiers (UDIDs), serial numbers associated with every mobile device. The complaint states that Apple allows UDIDs to be displayed to application developers and allows downloaded apps to access the user's browsing history whenever the user clicks on an ad or application using his or her mobile device.

"Consequently, anyone who has used a mobile device to browse the Internet to obtain advice about hemorrhoids, sexually transmitted disease, abortion, drug rehabilitation, or care for the elderly; to search for jobs, seek out new romantic partners, engage in political activity; in fact, to do more or less anything; can be reasonably sure that the browsing history created by such investigation has been incorporated into a detailed dossier for sale to marketers," the complaint says.

The complaint goes on to cite a Wall Street Journal investigation that found 56 out of 101 iOS and Android apps tested transmitted UDID numbers without authorization or consent. It also cites an academic paper published last year that found 68% of apps tested transmitted UDIDs.

The UDID is effectively a "super-cookie," the complaint alleges, and Apple fails to inform users about it in its privacy policy. In fact, the complaint states, Apple specifically disavows the sharing of personal information with third-parties for marketing purposes. As such the company's privacy policy would be more accurately described as a disclosure policy, the complaint suggests.

The key issue here is whether UDID numbers are actually deemed to be personal information. It's not entirely clear that they are. Eric Goldman, associate professor of law at Santa Clara University School of Law, said in an e-mail that there has been a flood of lawsuits in recent months over the disclosure of unique identifiers. He pointed to Facebook, which is being sued over its disclosure of Facebook's user ID numbers in its URLs. (In response to privacy concerns, Facebook has proposed encrypting user ID numbers.)

Goldman says that before the merits of the case can be evaluated, a number of questions have to be answered. "Does disclosing a unique ID actually disclose anything 'private' or otherwise legally protected?" he asked in an e-mail. "Did the users expressly or impliedly consent to the disclosures? Perhaps most importantly, did the users suffer any legally cognizable harm? Courts have been suspicious of privacy lawsuits where the consumer's only 'harm' is that the company made a contrary promise."

According to Andre Rado, a partner at Milberg LLP, the firm representing the plaintiff, UDID numbers do represent protected personal information.

"Privacy is 'protected' under the California constitution," Rado wrote in an e-mailed statement. "Transmission of the UDID would allow the recipient to identify exactly what a user is browsing and, together with other information, where they are at any given time. In addition, there are are disclosure-based and contract-based claims in the action."