When lightning occurs, it's a good a idea to have any electrical wires disconnected from the computer or wall. That includes phone line to the modem. Make sure you shut down your computer properly. Make sure all electrical plugs are unpluged from the wall or computer. Make sure that any phone lines connected to the modem be disconnected.
Lightning can go trough phone lines quite easily.
The best way to make sure that everything is safe, is that everything is unplugged and disconnected.