Passwords are strongly one-way encrypted in v7 but were clear text in v6. This is for security reasons and means that even if your v7 database has been compromised not only are the passwords not visible but they cannot be decrypted either (at least not easily or quickly).
As v7 differs considerably from v6.34 there are some features you must fine tune / set for yourself using Admin. The primary objective in designing the Migrator was seemless migration of Forums, Topics, Threads and above all Users together with correct encryption of their Passwords.