As the past participle and past-tense form of hang, hung is the correct word in all contexts not having to do with punishment or suicide by hanging. Hanged implies an intent to kill by hanging someone (or oneself) by the neck.
Examples
For example, these writers use hung in appropriate contexts:
A column of smoke visible from six miles away hung over the scene throughout the afternoon. [NBC Washington]
Two teenage boys that hung on to tree branches for two hours in the middle of Beaver Creek have been rescued. [My Fox Phoenix]
I hung the decorations in our platoon office for everyone to enjoy. [Galesburg Register-Mail]
When someone is hung out of malice but with no intent to kill, hung is the correct word—for example:
They hung him by chains and tortured him. [Day Press News]
And these are examples of hanged used well:
The hangman, who has hanged nine people in his 21 years in prison, has requested anonymity. [BBC News]
A man due to be sentenced tomorrow for murdering his brother has been found hanged in his cell. [Mirror]
