Window film provider Pentagon Protection has confirmed that security systems provider Westminster Group made a preliminary bid approach last week.Pentagon said the indicated offer was at a level which, in the opinion of the Pentagon board, substantially undervalues the company. Westminster's offer terms placed a value on Pentagon shares that was considerably lower than the prevailing market price at the time the approach was made; since news of the bid approach became public, Pentagon's shares have surged higher still.'The board considers that this initial approach fails to reflect the clear value in Pentagon and the material progress it has made over the past 12 months,' a Pentagon statement said.Pentagon shares have quadrupled in price over the last 12 months.