What I don't get is, once they had fairly quickly figured out it was due to a software update - why did it still take them 20(?) hours in total to roll it back to the previous version and get it back up and running? They both seem incompetent between them.
Bearing in mind the number of network devices affected it could be due to a number of things:
1. In order to avoid tampering the devices have to check in to obtain the latest update, just like mobiles and other devices that do this the roll out is staggered to ensure that resources such as servers and bandwidth are not overwhelmed.
2. Unless the software is self signed they'd need to obtain the certificate, sign the new package and test it before pushing out (they had more than enough Egg on their face, a duff release is something that they wouldn't want)
3. Assuming there is no auto-update, once the tested package had been supplied to the operator customers, they might have had to get to some sites to install it by plugging directly into the equipment in the cabinet (though I think this is unlikely these days unless it rendered the kit completely unresponsive to remote management by the various network NOCs.