Just got sent this by Rick Williams...
Security researchers have found what they say is an entirely new kind of web-based attack, and it only targets the Ajax applications so beloved of the 'Web 2.0' movement.
Vulnerable frameworks include: Microsoft ASP.NET AJAX (aka. Atlas), XAJAX and Google Web Toolkit, Prototype, Script.aculo.us, Dojo, Moo.fx, jQuery, Yahoo! UI, Rico, and MochiKit.
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Very useful for developing web apps, and like all good things, potentially dangerous in the wrong hands
A lot of people I know use Tamper, but I prefer Charles (great great app!), ServiceCapture is also good.
I've been doing an awful lot of JavaScript+XML loading recently (*shudders*), and without Firebug (a truly amazing Firefox plugin) I think things would be a lot worse.
The requirements for more visually exciting things are really starting to strain poor JavaScript 1.5 and the chewing gum and sticky tape approaches that are widely accepted.