A hacking collective said it successfully attacked the world's largest oil company - and is threatening to strike again.
Saudi Aramco, the biggest oil producer on the planet, was reportedly forced to quarantine thousands of infected PCs from its other systems after the onslaught.
The hacking group - which calls itself the "Cutting Sword of Justice" - said that it had destroyed as many as three-quarters of the company's computers on August 15. That would total at least 30,000 machines.
Saudi Aramco has not confirmed or denied that the attack took place, but said it has experienced "a network disruption".
In a statement the company said that "the company's specialised technical team immediately responded to restore service" and "confirmed the integrity of its electronic network that manages its core business".
The hacking group has posted data including hacked IP addresses which the New York Times said might lend credibility to their claims.
And in their own statement, posted online, the group said the company should expect to see another large-scale attack as soon as Saturday.
"We, behalf of an anti-oppression hacker group that have been fed up of crimes and atrocities taking place in various countries around the world, especially in the neighboring countries such as Syria, Bahrain, Yemen, Lebanon, Egypt and ..., and also of dual approach of the world community to these nations, want to hit the main supporters of these disasters by this action.
One of the main supporters of this disasters is Al-Saud corrupt regime that sponsors such oppressive measures by using Muslims oil resources. Al-Saud is a partner in committing these crimes. It's hands are infected with the blood of innocent children and people.
... This is a warning to the tyrants of this country and other countries that support such criminal disasters with injustice and oppression. We invite all anti-tyranny hacker groups all over the world to join this movement. We want them to support this movement by designing and performing such operations, if they are against tyranny and oppression."
It is not known precisely who is behind the attacks, with some speculating a foreign government such as Iran might be sponsoring the hackers.
Security expert Rob Rachwald, from the firm Imperva, said the attack was unprecedented:
"The Saudi Aramco attack is the first significant use of malware in a so-called hacktivist attack.
"In the past, hacktivists have typically used application or distributed denial of service (DDoS) attacks - in which they clog a website with traffic until it goes offline. However, the attack on Saudi Aramco is the first significant use of malware in a hacktivist attack. Hacktivists rarely use malware, if other hacktivists jump on this trend it could become very dangerous."