I know a little bit about it. Hammer and Scorecard were designed to interfere in the elections of other countries. (Oh, yeah, we do that a lot). It's kind of like when bank and stock transactions are made, there is always fractions of pennies that get left behind because of rounding. If might be 3/100th of a cent in one transaction, 7/100th on another, and so on. You can have a computer program collect all this fractions, from millions of transactions, and it adds up. It will never be discovered unless there's a deep digital audit that discovers it. Which is what happened 30 years or so ago when it was discovered, and banking systems were changed to prevent that from happening.
I stunt know if the penny robbers got the idea from someone in the CIA, or the other way around. But it was back in the late 80s and early 90s when computers were becoming more a part of the critical operations in business, finance in particular.
Hammer and Scorecard do essentially the same thing (I'm over simplifying) where lots and lots of votes are changed, but at a rate so small as not not attract attention. In a close election, like in battleground states, it doesn't take much. Just change 1 or 2 or maybe 3 votes or if every 100 counted, age you've got a 1-3 percent vote swing that can swing an election.
I certainly have no way of knowing if it was used in our elections, but I heard people in 2012 wonder if it wasn't tested out on a small scale then, knowing that Romney wasn't going to beat Obama. And I heard it might have been tested on a larger scale in 1016, but not really in earnest since Trump wasn't going to beat Hillary, not even close.
But if it worked well enough in 2012 and again in 2016,seems like a no-brainer to use it in 2020 when the chances of getting caught are just about zero, and the consequences of allowing an unfettered, legitimate election take place could give Hitler another four years in the White House, and that's just not even an option.
A full digital audit or a full hand recount would expose the fact that that, or something like it happened, but you still couldn't prove it, because there wouldn't really be anything to point to.
But if something like that did happen, it would certainly explain a lot.