Saudi Arabian Oil Co (Saudi Aramco) said its computer systems had been shut down by a virus late, but it added that production had not been affected.
"An official source of Saudi Aramco confirmed that it had isolated electronic systems for the entire company today and cut off external access as an early precaution," said a statement in Arabic from the company.
The world's biggest oil company said that although the virus affected some computers, it did not penetrate key components of the network, which it said would return to normal operating mode soon.
"The source ... reiterated the lack of any effect at all on the work of production due to the strength of advanced protection systems," the statement added.
Rumors had spread among traders earlier on Wednesday that the state-owned company had been subjected to a hacking attack.
