Students at the Acton-Boxborough Regional High School were dismissed from classes on Friday because of a bomb threat. Police responded to the school early Friday afternoon after receiving reports of several threatening messages found in one of the girls’ bathrooms, Acton Police Chief Francis J. Widmayer III said. Police searched the building and determined the school was in no danger. Authorities continued their search with specially trained dogs, Widmayer said.Todd Feathers can be reached at email@example.com. Follow him on Twitter at @ToddFeathers.