They somehow got hacked
not really hacked, but someone made a script that, well, here,
www.reddit.com/r/programming/comments/cluc5/html_injection_vulnerability_in_youtube_comments/
( ,
Sun 4 Jul 2010, 15:19,
archived)
www.reddit.com/r/programming/comments/cluc5/html_injection_vulnerability_in_youtube_comments/