Dim cmd as New OleDB.OleDBCommand
cmd = con.CreateCommand
cmd.Commandtext = "SELECT COUNT(ID) AS Anz FROM Personen WHERE ID = " & (ID des _
  ausgewählten mitarbeiters) & " AND Passwort LIKE '" & txtPassword.Text & "'"
if cmd.ExecuteScalar <> 1 then
    MessageBox.Show("falsches passwort")
end if