Lots of echo-chamber talk about the same information. I haven't seen any new information since the original postings.
My guess is that it would be rather difficult for even nation-state hackers to demolish the US IRS mainframe-based Individual Master File https://en.wikipedia.org/wiki/Individual_Master_File which is still mostly written in Cobol and assembler.
You would start by spreading rumors of impending coordinated multi prong attack at all storage facilities, simultaneously your inside man proposes relocating archives to a safe central location or just sending them all to a recovery facility.
FTS is fairly modern and well-funded. It's an example of Russian government infrastructure run by "young technocrats" (as opposed to Yes-men from Army and Ministry of Internal Affairs).
That's ФТС, the Federal Customs Service, which is closer to siloviki-style of management and career opportunities/incentives.
(you should search for ФНС)
It's an entry-level position, definitely not equal to lead security engineer. This person won't be responsible for backups redundancy.
Back on topic, as of early 14.12 UTC (the news were from 12.12), nalog.ru seems to be working just fine. Paid some property taxes to test. Keep up the good work, Defence Intelligence of Ukraine. Better luck next time.