if you run into anyone trying to discount the severity of the lastpass breach by saying the master keys are impossible to crack, ask them how lastpass' key derivation works, what a credential stuffing attack is, and how well PBKDF2 scales on GPUs.
given the details, it looks like anyone whose data was in the breach and who also reused their master password elsewhere is in imminent danger of having all their passwords compromised, as is anyone who used a relatively common password.

