Back in August 2011, Apple announced that it was phasing out developer access to unique device identifier (UDID) and requested developers a unique identifier specific for their app.

There have been some privacy concerns raised with the way Apple and app developers use UDID. Apple and some developers have also been sued for it, which had probably prompted Apple to enforce this change.

While developers could still access the UDID, Apple had given them time to figure out an alternative mechanism. It looks like that time has expired as TechCrunch reports that Apple has started rejecting apps that are still using UDIDs.

But this is the first time Apple has issued outright rejections for using UDIDs.

“Everyone’s scrambling to get something into place,” said Victor Rubba, chief executive of Fluik, a Canadian developer that makes games like Office Jerk and Plumber Crack. “We’re trying to be proactive and we’ve already moved to an alternative scheme.” Rubba said he isn’t sending any updates until he sees how the situation shakes out in the next few days.

UDID is an alphanumeric string unique to each device based on various hardware details. You can find the UDID of your iOS device from iTunes by connecting your it to the computer, selecting the iOS device from the list of devices in iTunes and then clicking on the Serial Number in the Summary tab.

While UDIDs have been used by ad networks to better understand user behavior, it has also been used by developers for anti-fraud checks.

Most developers should have seen this coming, but it would have been nice if Apple had sent them a month’s notice before rejecting the apps.