Police are investigating after a dog attacked its owners over the weekend in southwest suburban Plainfield.  Authorities say officers were called out Saturday night to a home on Judith Drive on reports of a dog bite.  The officers found a male pit bull and were able to gain partial control of it.  However, the canine was immediately euthanized because it was acting aggressively toward police and the owners.  Four people were bitten, including a man who was hospitalized with severe injuries to his arms.  The three other victims were treated for minor injuries.  An initial investigation found the attack was unprovoked.