Jquery plugin? Check if code exists on a website

Jquery plugin? Check if code exists on a website

Hi Guys,

I was hoping someone could suggest a solution for the following:

From a specific website, the user is able to "download" a script which will attach itself as an addon or something similiar to the browser.
From that point on, if the user browses to certain websites which we have added some code on the "addon" will detect that code on the website and redirect the user to a certain website.

I'd want to use this for some sort of competition, so the user signs up by installing the "addon" from my website, and then he will win a prize if he visits certain websites. Most website will redirect him to a site which says "Sorry, no prize was found on this site" but then certain websites will redirect them to a page saying "you have won a prize" based on the script that was found on that site.

I was wondering if anyone could suggest how I could go about this or/and offer an existing solution/plugin.

Thanks! :)