A WebmasterWorld thread named Yahoo is Altering Webmaster Content describes how Yahoo! has added a security feature that removes all JavaScript from the publishers. The security feature is a tagged known as "securty=restricted" which disables all javascript in Internet Explorer. That means any AdSense or JavaScript driven banners are stripped from the content.
Senior Member Cabbie says; "To me this constitutes blatant theft. For all purposes they are providing your content on your bandwidth and at the same time preventing you from getting a return. How can anyone buy anything while in a secruity restricted frame, when all cookies and java is disabled."
Forum discussion at WebmasterWorld.