Complex sentence: The festival website was hacked and festival information replaced with the Chinese flag and anti-Kadeer slogans, and booked out all film sessions on the site; a denial-of-service attack forced it to shut down.
Split into simpler sentences: The festival website was hacked and festival information replaced with the Chinese flag and anti-Kadeer slogans. All film sessions were falsely shown as booked out on the site, and a denial-of-service attack forced it to shut down.