MoPub, a mobile ad company, claims that Apple's policy of rejecting ads which utilize unique device identifiers (UDID) is resulting in an ad revenue loss of 24 percent for iOS developers. MoPub arrived at this finding after analyzing three months worth of ad data spanning billions of impressions from their own ad network.

The data provides evidence of how a world without ad conversion data from UDID (or an appropriate substitute) could hurt revenues for developers. It found publisher inventory with UDIDs that were sent to advertisers earned an average eCPM of 0.76 cents, compared to 0.58 cents for those ad impressions without the unique device identification, representing a 24% lower eCPM.

Source: press release

A device's UDID, as the name implies, identifies a device. By extension, it can also be used to identify the user's unique presence online and – when combined with the right information – can even be used to personally identify that user. Unlike a cookie though, a UDID cannot be deleted or changed, so once someone links a UDID to you and what you are doing online, the cat's out of the bag. As a result, Apple had barred the use of UDID strings by advertisers almost a year ago. Interestingly though, as MoPub points out, Apple isn't doing a very good job at catching developers who continue to submit apps which break the rules.

Apple's recent response to UDID usage has raised concerns among thousands of app businesses that could be affected if conversion tracking data is not available, particularly developers of free apps that rely on advertising as their primary source of revenue. With no apparent option from Apple in sight, players across the mobile ad ecosystem are pursuing several different alternatives, increasing fragmentation in an already fragmented industry. While some developers are continuing to use UDID data until Apple's position is clear, others are removing UDIDs and other data designed to help ad performance and pursuing one of four short-term solutions.

It probably doesn't surprise most that a mechanism which can be used to better identify a person carries intrinsic value to advertisers. But it is interesting that MoPub has managed to actually assign it a monetary value. Although we've heard firms say iOS is more lucrative than Android, some developers may still be discontent with squandering potential ad revenue.

In terms of advertising, MoPub also discusses some third-party solutions to the UDID problem but points out that no solutions exist that universally address conversion tracking needs at scale and address government privacy concerns. Until then, some developers will continue to risk using UDID data in their ads while others will shy away from the practice and take a 24 percent hit.