Marriott InternationalChief Executive Arne Sorenson apologized on Thursday before a US Senate panel for a massive data breach involving up to 383 million guests in its Starwood hotels reservation system and vowed to protect against future attacks. Sorenson told the Senate Permanent Subcommittee on Investigations that the hacking, which occurred over a four-year period, prompted the company to accelerate the retirement of the Starwood reservation system that was completed in December.