Beginning with the individual who made that statement, all the way up and down the chain of IT IRS "experts" maintaining the system should be suspended without pay immediately, with firings to follow. All of them.
No large business or enterprise lacks redundant systems to prevent exactly what they are claiming. The biggest business of all, the Federal government, lacks those safeguards?
Fire them all and remove their pensions. This is a years long criminal enterprise, and the RICO laws should apply. As an general and just rule, criminals should NEVER profit from their crimes.
You pretty much nailed it. This is not an acceptable excuse these days.