A tool for verifying that a message received by a social networking service was sent by a bona fide owner of a social networking account who purportedly sent the message. The tool receives a message and it locates in the message a string that was entered into a message text field of the message. The string is compared with a registered authentication string for the bona fide owner of the account. If the string in the message matches the registered authentication string, the string is removed from the message and the message is forwarded to the social networking service. If the string in the message does not match the registered authentication string, the message is blocked from being forwarded to the social networking service.