A$.$

Decrease the clipping level, that is$,$ the number of failed logon attempts permitted before a user account is locked out.

B$.$

Decrease the auto$-$logout time, that is$,$ the maximum time a user is allowed to be inactive before he$/$she is automatically logged out because of inactivity.

C$.$

Test all passwords against a password dictionary.

D$.$

Ask all users to change their passwords immediately