Ah, Arasaka had backups. That's why Militech used a tactical nuke on the tower... Which set off the bigger nuke in the tower...
The net was rebuilt with the 'wotsit-called' algorithms, (can't remember the names,) something 'grubs
Iharu-Grubb Transformation, Chris. What lets Net users "see' the "consensual hallucination that is cyberspace". The IGT didn't build the Net, but they did change the perspective for users, for the whole Net. And they affected everything. And Rache had an in.
Arasaka is based out of Japan, the arasaka towers attack really would have accomplished very little.
True, Arasaka was based out of Japan - then the Japanese nationalized them. Heh heh heh. I'd say a politician did more with his pen than a nuke did. Anyway.
That nuke didn't bring down Arasaka or the Net.
"Anybody with brains" do have backups. All major server networks, all ISPs, everyone has backups. DoD has even more, very well protected.
But you have to keep them backed-up, or they lose their value. And when you do back them up, they become vulnerable to infection. It's a real issue for security pros. Of course, they are quite good about protecting their stuff, although cutting edge is still a war between the big private companies like Symantec, McAfee and, well, the hackers. Actual black hat hackers. Who are, actually, very good. They crack the uncrackable, decrypt the unbreakable.
Some are geniuses. These people will become the Netrunners of tomorrow. And in Cyberpunk 2020, of these geniuses, the very best was Rache Bartmoss. I man who, as in my favourite definition of genius, "redefined his field".
It is far from implausible a suitably brilliant mind, motivated and equipped, could bring down the Net and corrupt the safeguards.
Just an "average hacker" shut down a NJ naval station, responsible for resupply, for a week, locking off emails for another 3 weeks. http://www.computerweekly.com/feature/Average-hacker-skills-shut-down-US-defence-systems
And that was basically a script kiddie, not a black hat. That naval weapons station was responsible for supplying the US Atlantic Fleet. Yeah.
So could Rache, a guy who helped build the Net, shut it all down and screw the backups, safeguards and redundancy measures? Yes, absolutely yes. Did he, in 2020? Yes he did.
Will he, in the real world? We may yet see.