Request for password

I keep being prompted for a password when I open Thunderbird ...."Enter your password for [email]@outlook.com on imap-mail.outlook.com:" but I don't recall ever setting up a password and don't know what it is. I am unable to access my e-mails via Thunderbird without entering a password. Shortly before this problem arose on 22nd October, I received an e-mail from Microsoft advising that they had detected unusual activity on my account and they had blocked access to my inbox, contacts and calendar. I went through the process of changing my password with Microsoft and I can now access my e-mails through Outlook.com but not through Thunderbird. I'm not sure if the problem I had with Microsoft has caused the passsword prompt for Thunderbird to appear.