Five hospitals operating in Massachusetts are under investigation for possible billing fraud by the Department of Justice. In a Securities and Exchange Commission report, justice department officials said its investigating five Massachusetts hospitals, among others across the country. The Massachusetts hospitals include: Arbour-HRI, a 66-bed facility in Brookline; Arbour Hospital, a 136-bed psychiatric facility in Jamaica Plain; Arbour-Fuller Hospital, which has 103 beds in South Attleboro; the 120-bed Pembroke Hospital; and Westwood Lodge Hospital, with 89 beds in Westwood. All are owned by Universal Health Services, a Pennsylvania-based company that is the largest provider of mental health services in the state.