With the scrutiny from Congress around privacy issues, Apple has started rejecting apps that access UDIDs, Unique Device Identifier Numbers that are unique to every iPhone and iPad, reports “TechCrunch” (http://techcrunch.com/2012/03/24/apple-udids/).

Six months ago, the company gave developers a head-up about this via iOS documentation. But this is the first time Apple has issued outright rejections for using UDIDs, according to “TechCrunch.”

Because the UDID is unique to each iPhone and iPad, it can provide a means for third-party advertisers looking for a way to track a mobile device users’ online activities. Because the UDID is not alterable or deletable by a iPhone or iPad user, some have referred to the UDID as a “supercookie.”

Such tracking has caused concerns among privacy advocates because it could give personal information about users without their knowledge. On the other hand, the change removes a way for makers of apps, advertising networks, social game networks and analytics firms to easily offer their services, notes “The Journal.”