I migrated 9i DBs to 10g.
After migration, clients complained that some of their accounts were locked.
In 10g, FAILED_LOGIN_ATTEMPTS in default profile was changed from UNLIMITED to 10.
This is the cause of problem.
I suggest to create new profile before migration and set all users with default profile to the new profile.
New default profile can be something like this :
CREATE PROFILE NEW_DEFAULT LIMIT FAILED_LOGIN_ATTEMPTS UNLIMITED;
select 'ALTER USER ' username || ' PROFILE NEW_DEFAULT;' from dba_users where profile='DEFAULT';