Here’s an interesting article on Ajax Applications and security. It won’t be long before content hijackers take over your XML data which you’re using for your Ajax applications.
If data is more openly available as XML over HTTP, it’s going to be pretty damn easy for a smart hacker to get access to that data to make applications like this impressive example… which is great, but undoubtedly someone eventually will feel like their data is being “stolen” or “misused”. 

Link: Whirlycott - Philip Jacob » Security in an AJAX World