Private Sub Worksheet_Change(ByVal Target As Range)
Dim val As Variant
' Exit sub if multiple cells updated at once
If Target.CountLarge > 1 Then Exit Sub
' Exit sub if update is not in 1st column
If Target.Column > 1 Then Exit Sub
' Check to see if entry is equal to values in new two columns in same row
If Target <> "" Then
val = Target.Value
' See if value is found in column B
If Application.WorksheetFunction.CountIf(Columns("B:B"), val) > 0 Then
' See if value is found in column C
If Application.WorksheetFunction.CountIf(Columns("C:C"), val) > 0 Then
' Pop up message box alerting user
MsgBox val & " is found in columns A, B, and C", vbOKOnly
End If
End If
End If
End Sub