YouTube is currently number 4 of the most visited websites on the planet
according to Alexa. With more than 100 million video views every day, visitors are at great risk due to a serious cross-site scripting vulnerability, from which YouTube suffers for a month already. It is a query string XSS that appears in the video viewing page. Works only with IE and probably Konqueror. Malicious people can use it to spread malware, steal cookie based authentication credentials and redirect unaware users to phishing scam pages.