WebKit in Apple iOS before 9.3 does not prevent hidden web views from reading orientation and motion data, which allows remote attackers to obtain sensitive information about a device's physical environment via a crafted web site.
https://support.apple.com/HT206166
http://www.securitytracker.com/id/1035353
http://lists.apple.com/archives/security-announce/2016/Mar/msg00000.html