Apple's multi-device ad network iAd can now tell advertisers if users are engaging with their messages. The tweak to iAd was not announced by Apple but was first mentioned in a blog post on mobile ad analytics site HasOffers. "Apple has kind of been like the sleeping giant on the sidelines of the mobile advertising space. You haven't seen much from them. This now has the potential to change how ad networking works," said Ray "R" Wang of Constellation Research. By the end of 2016, mobile advertising is expected to reach $24.5 billion, Spectrum Research says.