This isn't completely conclusive, but I was able to replicate what happened to Anthony Weiner without hacking any passwords, via this blog:
http://cannonfire.blogspot.com/...
All I did was create a yfrog account and tie it to a Twitter account. Then I emailed, from a TOTALLY different email account, a picture, with nothing in the subject and @unabogie in the text.
yfrog posted this image to my list of photos, and also POSTED IT TO MY TWITTER FEED without any additional action from me.
Here are the results:
http://twitter.com/...
Just thought I'd get the word out.