A major Mexican newspaper was attacked for the second time this month when two masked men set its offices on fire. The men threatened a security guard at the Monterrey office of the El Norte paper before pouring gasoline and sparking a fire Sunday. No one was hurt, according to the paper. Though no one has claimed responsibility for the attack, kidnappings, killings, and other threats against journalists have become frequent since the start of Mexico’s drug war. Seventy journalists have been killed in Mexico since 2000, and 98 percent of those murders have gone unsolved.