Well, seems like there's one way...
Maybe I'm being silly, but I think if they searched their database for an account emails similar to his they'd probably find it. Not sure if that would violate some privacy laws though.
A cross-site scripting (XSS) flaw on Yahoo! Mail creates a means to steal cookies and hijack accounts, according to a hacker who is offering to sell an alleged zero-day vulnerability exploit for $700. The cybercrook, who uses the online nickname TheHell, knocked up a video to market the exploit which he is attempting to sell …