Not just employees, but also "subjects, witnesses, and complainants". Yikes. This is way worse than the last one.
I've lost track now.. which one do you mean?
The OPM breach of the SF-86 database is still the worst and most catastrophic that I'm aware of. That was larger (millions), was the result of background checks (aka blackmail fodder), included full read/write access (tainted?), and likely every position that required a clearance outside the CIA.
This one seems especially terrible because it had information on people unrelated to the US government.
*I had a Secret 10+ years ago.