Charlotte McKinney -- I Was Hacked!

Charlotte McKinney did NOT choose to share her boobs with the world -- instead she was the victim of hackers ... according to her rep.

On Wednesday night ... a topless pic was posted on her Instagram -- instantly grabbing the attention of her 500,000 followers. It included the caption, "I'm gonna be so damn hungover tomorrowww" -- making it seem like she'd just wrapped a night of drunken fun, and decided to get naked for fans.

But her rep tells TMZ ... "Charlotte has once again become a victim of hacking. It is disgusting someone does this and hopefully laws will change to protect people from these cyber attacks."