A flight from Los Angeles International Airport to O'Hare International Airport in Chicago received an online threat early Tuesday afternoon, the fourth day in a row that an online threat was made against an aircraft, NBC News reported. On Saturday, two planes were escorted by fighter jets to Atlanta's airport after bomb threats were made via Twitter. A day later, a Delta Air Lines jet from Los Angeles to Orlando was diverted after another threat was made on the site. On Monday, several bomb threats targeting Southwestern flights popped up online. FBI officials have expressed concern regarding the increase in online threats that now number more than a dozen overall. "All threats are taken seriously and will be investigated," The FBI said in a statement.