In recent months, hoaxers playing online games have allegedly used proxy servers and other high-tech identity-disguising tools to anonymously threaten schools online or in phone messages with electronic voices to trigger a huge police response, including SWAT teams. Some officials described Monday's threats as automated or robotic and at least two — at Lakewood High School outside Denver and at Ben Franklin Elementary School in Rochester, Minnesota — came in just before noon local time. [...] students at Murray High School outside Salt Lake City were sent home and bomb-sniffing dogs were brought in.