I'm not here to defend LastPass, but there are some rational answers to the questions you're asking, a lot of them having to do with human psychology.

First thing's first, and yes I am "victim blaming" when I say this: 60% of users reuse their passwords. [0,1] It's a widespread problem. Maybe that number is lower for a technical site like HN, but I have encountered technical people who do not practice what they preach.

>how the heck would they know which passwords are compromised, if it wasn't a compromise on their end?

You can check for a compromised password the same way you check if a password is valid, both without having stored the original password in plaintext. You have a list of known-compromised hashes and see if the hashed password is in that list. [2]

>For everyone whose account was protected by blocking access from odd region, how many are there whose accounts were quietly accessed and no email was shot off to warn the owner?

None based on my experience with the service. Each time you login from an unrecognized device or IP, you receive an email and have to confirm the login. It's good hygiene to check the access logs, although I've been dirty in that regard.

>They are claiming that the master password was used on some other (compromised) service, but they provide zero evidence for this. And if they don't know your passwords, how on earth do they know that you've reused them on a compromised service? Can they name that service?

No. And they probably won't ever be able to. And probably neither will anyone else. See [2].

>That is true, but there are so many reports now that it's really hard for me to believe they were all dumb enough to reuse their master passwords elsewhere and are also bullshitting us on HN.

Well I can imagine a few things going on. Like that 60% reuse number in [0], there are probably a lot of people who did reuse their master password. I'd be embarrassed myself to admit I reused a password and it got compromised (correction: I have reused passwords and have been compromised, luckily not in a damaging way). You're kind of exemplifying that point by calling someone who would do that "dumb enough".

The other group of people who really didn't reuse their passwords may have done something I did a few weeks ago - forgot I was connected with a VPN. I SSH'd into a server, saw a weird IP and freaked out. Then after 15 minutes of investigation, I realized duh I was just connected through a VPN in Europe.

>bullshitting us on HN

I'd be careful about this assumption. I have seen people bullshitting here. I won't go as far as outright denying that people haven't reused their passwords, but I am always a little skeptical of things like this (i.e. where people say one thing because they're embarrassed about being associated with the other). It has certainly heightened my senses.

>I don't think we have a "smoking gun" or a site/service/extension that is common to everyone who reported this thing happening to them.

As has been theorized elsewhere, it's very possible we're seeing early signs of the results of the log4j exploits.

I'm in wait and watch mode to see if LP really is compromised.

[0]: https://spycloud.com/password-reuse/

[1]: https://www.troyhunt.com/password-reuse-credential-stuffing-....

[2]: https://haveibeenpwned.com/Passwords A password from my late childhood to early teens shows up 150 times