When I open a form in access I need a message box to appear if there is certain criteria in one of the fields in the record

eg. If when the form is opened the field 'status of debt' contains the letters CU then I need a box to appear saying "This is a court debt please pass to etc etc"

The field may contain the letters CU CT or CU IN so the box needs to appear when the letters CU are in the field not when the field = CU.

Is this possible? Whats the code and where do I put it?

Cheers