If your webhosting turned register-globals off and you are still using a script/software which requires register-globals on you have a problem. But there is an easy solution: Just put this code at the top of your php script(s). Attention!!! "register_globals=on" means a huge security risk. Do not turn it on unless you know what are you doing!
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You can improve this to build a small web-firewall and prevent sql-injection etc. You can add some code and strip unwanted html-javascript tags with this.
Having register_globals = on
Having register_globals = on does not mean a huge security risk. Also, the provided code does not emulate it properly so instead consider using an example from the manual:
http://php.net/manual/en/faq.misc.php#faq.misc.registerglobals
extract($_REQUEST);