Well, it's probably cost them over a $billion in lost trade today, plus whatever business they loose from pissing off clients for not giving warning of the maintenance.
yeah it doesn't add any positivity to their ratig thats for sure
lost trading revenue,reputation loss and the upgrades often last longer than declared too
maybe that system upgrade is just a pretext tho,they are targeted by hackers thats for sure
maybe they got tipped off that there is a vunerability in their security or something similar
I do not believe in sudden,no warning maintenances mid of the week