The Top Sites feature in Apple Safari before 9.1 mishandles cookie storage, which makes it easier for remote web servers to track users via unspecified vectors.
https://support.apple.com/HT206171
http://www.securitytracker.com/id/1035354
http://www.securityfocus.com/bid/85055
http://lists.apple.com/archives/security-announce/2016/Mar/msg00005.html