Brussels, Sept. 22 -- The fallout from a cyberattack that crippled check-in systems at several European airports stretched into a second day on Sunday, with passengers facing dozens of cancelled and delayed flights amid ongoing uncertainty over who was behind the security breach. Brussels Airport, seemingly the hardest hit, said it asked airlines to cancel nearly 140 departing flights scheduled for Monday because a U.S.-based software system provider "is not yet able to deliver a new secure version of the check-in system." The airport said 25 outbound flights were cancelled on Saturday and 50 on Sunday. Heathrow said early on Sunday that work was continuing to recover from the check-in system outage. It added that "the vast majority of flig...