Unsuccessful Login Attempts

public DateTime GetDt
{
    get {
        if (ViewState["GetDT"] == null)
        {
            ViewState["GetDT"] = DateTime.Now;
        }
        return (DateTime)ViewState["GetDT"]; }
    set { ViewState["GetDT"] = value; }
}
public int CNT
{
    get
    {
        if (ViewState["CNT"] == null)
        {
            ViewState["CNT"] = 0;
        }
        return (int)ViewState["CNT"]; }
    set { ViewState["CNT"] = value; }
}

protected void uxLogin_Click(object sender, EventArgs e)
{
    SqlDataAdapter ad = new SqlDataAdapter("select 1 from x where Uname='" + uxTxtUserName.Text.Trim()+ "' and PassWord='"+uxTxtPassword.Text.Trim()+"'", con);
    DataTable dt = new DataTable();
    ad.Fill(dt);
    if (dt.Rows.Count <= 0)
    {
        CNT = Convert.ToInt32(CNT) + 1;
        TimeSpan tm = DateTime.Now - GetDt;
        if (CNT > 3 && tm.Minutes < 5)
        {
            //Write code to show error msg.
        }
    }
    else
    {
        CNT = 0;
        GetDt = DateTime.Now;
    }
}