Apple Safari before 4.0 does not prevent calls to the open-help-anchor URL handler by web sites, which allows remote attackers to open arbitrary local help files, and execute arbitrary code or obtain sensitive information, via a crafted call.
http://lists.apple.com/archives/security-announce/2009/jun/msg00002.html
http://secunia.com/advisories/35379
http://securitytracker.com/id?1022345