"Account Grabbing"

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Somebody shared me her experience from one of the websites she has an account with,she was surprised to receive a message from one of her friends stating that somebody posted a picture using her account using her name and profile. Just imagine a different person with near obscene picture using your profile. I've heard of photo grabbing but account grabbing it's a serious matter. If anybody has any ideas as to how to resolve this problem,or even suggestions feel free to send your message.