This is a case where the web is only as secure as its most insecure link. Even if your site uses a hash to prevent abusing redirects people can still abuse the

This is a case where the web is only as secure as its most insecure link. Even if your site uses a hash to prevent abusing redirects people can still abuse them. They need only find a site that uses hashless redirects, generate some redirect link using that site, and then create a legit redirect link using your site. Blacklisting certain domain strings in the url would not solve this- new domains are too easy to obtain. Whitelisting would help but may be prohibitive depending on what you are building...