Websites belonging to several state-backed Iranian oil firms have been targeted by a group of hackers from Saudi Arabia, PANA News, a Persian-language news agency reported. Websites for Iranol, Iranian Oil Ministry, National Iranian Oil Company were all targeted by a computer worm on April 22, but it was detected before it could affect the systems, the agency said. A worm is a computer virus that is capable of self-replicating in order to spread deeper into a computer system. The incident is not the first time that Iran, the world’s second largest OPEC oil producer, has been targeted in cyber attacks. The Islamic Republic’s state-controlled media reported last month that the country’s oil industry had the victim of a major cyber attack. Iranian Oil Ministry, the National Iranian Oil Company and a number of other government-owned entities were targeted by a computer worm, it said. In 2010, the government revealed that it had discovered a virus known as \'Stuxnet\' buried within centrifuges at the country\'s nuclear facility in Bushehr. The application, or \'malware\' as malicious computer code is referred to, was apparently designed to cause severe damage to the country\'s nuclear energy programme. Iranian authorities appeared to nullify Stuxnet before it achieved this aim. The Islamic Republic\'s nuclear enrichment programme has been a major source of contention for the US and its allies, leading to stringent sanctions being placed on Iran which have eroded its stance as a major oil exporter. Iran insists that its nuclear programme is for civilian purposes, although many Western governments suspect the country may be attempting to enrich uranium to a military grade level.