Is there a command I can use to force everyone to use a different password, actually to send everyone an email with a new password so they will change it?

To add more, I went to send a new password to everyone manually but I get this error. That's why I asked for a command. [:"red"]Fatal error: Call to undefined function: headers() in /home/doording/public_html/ubbthreads/admin/adminmailpassword.php on line 94[/]
I have 6.4b1.

I don't think that adminmailpassword expanded user info mod will work in 6.4 as the mail function in threads was completely rewritten.... hence the undefined function.

You could use an SQL command to reset everyone's password - then they would have to use the "I forgot my password" link on the login page.

The passwords are one-way encrypted in the database, so they cannot be seen by anyone. So when you do the update, it won't work if you don't use the command to encrypt the new password.

UPDATE w3t_Uusers
SET U_Password = MD5('whatever')

Would set everyone's password to an MD5 version of 'whatever'.