I was just thinking about Battlestar Galactica (the newer series) and one of the themes is the vulnerability of advanced computers and computer networks and hubris they instill in their operators. Basically, in the beginning of the show the Cylons which are sentient robots stage a surprise nuclear attack on all the Colonies which consists of a dozen or so planets in a single star system.

The first stage of the attack is a computer virus that basically knocks out every single computer system that is networked. And the entire defense system of the humans is nullified. Their ships and fighters go dark and lose power and are just floating in space completely defenseless.

The two Battlestars that survive turn off all their advanced computers and disconnect everything from the networks. Everything has to be run old school manually like analog.

So real life possible occurrence?