Evitar el postback al pulsar un botón en ASP.Net

<asp:Button ID="Button1" runat="server" Text="Pulsa"
OnClientClick="return deshabilita();" />

<script type="text/javascript">

function deshabilita()
{
var btn = "<%= Button1.ClientID %>";
if (ValidatorValidate())
{
document.getElementById(btn).disabled = true;
return true;
}
return false;
}

</script>