Not everyone agrees. Some argue that a covert espionage operation has caused such delays that Iran still needs another three years to build a bomb. Sabotage efforts by Israeli, American and British intelligence have successfully slowed Iranian progress, most notably via the Stuxnet computer virus that caused the centrifuges at Iran's Natanz uranium enrichment plant to explode. Mossad agents on motorbikes are also believed to have planted magnetic explosives on the cars of at least two key Iranian nuclear scientists as they weaved through Tehran's traffic jams. Mohsen Fakhrizadeh, the scientist and Revolutionary Guards officer who is thought to be the ultimate mastermind of the nuclear programme, is now believed to be under round-the-clock protection as a result. But, whatever the time frame, some in Israel believe there is additional cause for urgency that could prompt military action sooner rather than later.