I have been in this situation, and you're correct. Somewhere in the organization, a product team is going to throw a fit about usability and churn over the dec

I have been in this situation, and you're correct. Somewhere in the organization, a product team is going to throw a fit about usability and churn over the decision to reset user passwords en masse, or to force users to change them when they first log in. This isn't a slight against product managers, but one of the clearest indications of a company's overall security culture "health" is how the security, engineering and product teams choose to compromise and "pick their battles." Risk accepting vulnerabilities has a legitimate place when you have to balance product development and usability, but so does pushing back on egregious issues. I don't have privileged insight into Yahoo's organization, but in this case it's pretty clear the security team should have either been more diligent in conveying the ramifications or less kneecapped by the surrounding org units, depending on the circumstance. More importantly, Yahoo should have "migrated" their passwords in the manner a parallel comment explains in this thread. This is what Facebook and other companies did after maturing their security programs (see "Facebook Onion" on how Facebook transitioned away from MD5). Also good to note - there is evidence Yahoo's security culture improved over the years. The decision to go with MD5 almost certainly happened in the 90s, and when Tumblr suffered a breach all users were forced to reset their passwords. The capability and awareness was clearly there.