Problem with Telerik RadMaskedTextBox

Question

Hi all
I am using RadMaskedTextBox for ssn Format

<telerik:RadMaskedTextBox ID="txtSSN" runat="server" SelectionOnFocus="SelectAll" DisplayMask="none"

                                    PromptChar="_" Width="200px" Mask="###-##-####" NumericRangeAlign="Left" BorderColor="#C4C4C4">

                                </telerik:RadMaskedTextBox>

But by default textbox showing masked message like ___-__-___ but i don't need by default.How to remove that
any one help me plz