Saudi Arabian oil giant, Saudi Aramco, said it has restored its main internal network services after a computer virus affected 30,000 work stations in mid-August.

Critical data on the company's PCs was replaced with the image of a burning American flag on 15 August, which Saudi Aramco described as a "malicious virus."

In a statement, Aramco said affected workstations been cleaned and normal business resumed on Saturday when employees returned to work following the Muslim Eid holidays.

Chief executive Khalid al-Falih said: "We addressed the threat immediately, and our precautionary procedures, which have been in place to counter such threats, and our multiple protective systems, have helped to mitigate these deplorable cyber threats from spiralling."

Hackers, who call themselves Cutting Sword of Justice, said they caused the virus, but Aramco said it is still investigating the causes of the incident and those responsible for it.

The company confirmed that its systems of hydrocarbon exploration and production were unaffected as they operate on isolated network systems.

Production plants were also fully operational as these control systems are also isolated.

Image: Saudi Aramco headquarters complex.