update users
set email = concat(MD5(RAND()), '@example.com'),
crypted_password = 'c51cb1acc88d17b00950fe1d116980cfabbdf96a',
salt = "44f553a7cc4b41dff01e8ec1d86b1fb9f8ee81be";

This gives every user a random example.com email address, and sets their password to “password”.

This is just an example, of course — you’ll run into reasons to do this slightly differently.

Mid-1960s
Later 1960s—Mid-1970s
Mid-1990s—2000s

There’s also a nice write-up of his Wigmore show on Joanne Mattera’s blog.