The BBC reports that 90% of the country's oil export network is now out of commission:
The computer virus is believed to have hit the internal computer systems at Iran's oil ministry and its national oil company.
Equipment on the Kharg island and at other Iranian oil plants has been disconnected from the net as a precaution.
Physical processing of Iranian crude hasn't been hit, but the ability to ship it out is more or less crippled. This is bad, as oil cash comprises the majority of Iran's budget. They are going to want to fix this very, very fast.
So who did it? The US, or Israel, or both, most likely—a la Stuxnet. No word on whether this virus of the same degree of sophistication as Stuxnet, but it was at least good enough to force Iran to hamstring its own national economy. [BBC]