…is just that: virtual. Any speculation that Stuxnet could trigger a thermonuclear explosion in Bushehr is completely unfounded. First, Stuxnet does not target Bushehr. Second, even if it did, it could not mess with the systems in the primary circuit. The funny thing is, the Russians know that very well.
If there is one thing that we can learn from the situation in Bushehr it seems to be that contrary to Iran’s statements from last year, Stuxnet seems to have infected not only office systems in the nuke plant, which seemed highly questionable already months ago. Second, it would certainly be a good idea for Iran to clean up all systems before going operational in Bushehr (and before resuming operations in Natanz) as any further attempts to remove the virus when the plant is running will be much harder or even impossible. As long as there is even a single system in the nuclear program still infected with Stuxnet, those centrifuges continue to be at risk.