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 the year — Lailat al Qadr, or the Night of Power — celebrating the revelation of the Koran to Muhammad.

That morning, at 11:08, a person with privileged access to the Saudi state-owned oil company’s computers, unleashed a computer virus to initiate what is regarded as among the most destructive acts of computer sabotage on a company to date. The virus erased data on three-quarters of Aramco’s corporate PCs — documents, spreadsheets, e-mails, files — replacing all of it with an image of a burning American flag.

United States intelligence officials say the attack’s real perpetrator was Iran, although they offered no specific evidence to support that claim. But the secretary of defense, Leon E. Panetta, in a recent speech warning of the dangers of computer attacks, cited the Aramco sabotage as “a significant escalation of the cyber threat.” In the Aramco case, hackers who called themselves the “Cutting Sword of Justice” and claimed to be activists upset about Saudi policies in the Middle East took responsibility.