Thumbs up - Meaning in the Arab World

I have read on a few blogs now that the pictures of Iraqis giving “thumbs up” to American troops or reporters were not all they seem. These sites claim that the thumbs up is in fact an offensive gesture in Iraq and other Arab countries.

The only thing I could come up with on Google was this.

Anyone know the facts on the matter?

An Iranian guy told me it means “fuck you”.

Clarification-

http://www.ooze.com/finger/html/foriegn.html

“*But in Iran, Afghanistan, Nigeria and parts of Italy and Greece it is an obscene insult, especially when combined with a sweep of the arms. It most places it roughly means, “Sit on my phallus, asshole,” and carries the same stigmatism as the middle finger. *”