I think "hacks" is a pretty strong word here. They're basically just brute forcing accounts with email and password combos that have been leaked from other sources.
That's why I am pro-password managers. Even if they're imperfect, password re-use remains a major active threat (contrast that with a lot of theoreticals against password managers).
Around ten of my accounts' information has been leaked (inc. big ones like Adobe). But I don't re-use credentials so aside from an uptake in spam, it has had no impact. Typically these were services I haven't used in years.