Iran says its nuclear program is just for keeping the lights on. The US (and others) say it's for making country-annihilating weapons. To be sure, the International Atomic Energy Agency's been keeping tabs—and say they've been digitally attacked.
The IAEA claims Iran gained access to confidential documents, and may have even tapped their phones by tampering with SIM cards, the Wall Street Journal reports. This is bad. The IAEA inspection program requires a degree of secrecy as to its methods—and who within Iran's program it's working with. If Iran knows who's working with the IAEA, they could become targets of the regime, and help. This is bad. The more Iran knows about how the world is watching its reactors, the easier it'll be for them to get away with a weapons program.