Saudi Aramco’s Khurais plant. A cyberattack wiped out data on three-quarters of Aramco’s PCs.Credit...Agence France-Presse/Getty Images The hackers picked the one day of the year they knew they could inflict the most damage on the world’s most valuable company, Saudi Aramco. On Aug. 15, more than 55,000 Saudi Aramco employees stayed home from work to prepare for one of Islam’s holiest nights of th