<input type="hidden" name="option" value="com_user" />
    <input type="hidden" name="task" value="login" />
    <input type="hidden" name="return" value="aW5kZXgucGhw" />
    <input type="hidden" name="036a53578a92ba65c60798bf6155208f" value="1" /></form>

 MatchCollection mc = Regex.Matches(richTextBox1.Text, "<input type=\"hidden\" name=\"option\" value=\"(?<option>.*?)\" />[\\s\\S]<input type=\"hidden\" name=\"task\" value=\"(?<task>.*?)\" />[\\s\\S]<input type=\"hidden\" name=\"return\" value=\"(?<return>.*?)\" />[\\s\\S]<input type=\"hidden\" name=\"(?<value>.*?)\" value=\"1\" /></form>", RegexOptions.IgnoreCase);
             
            string option = mc[0].Groups["option"].Value;
            string task = mc[0].Groups["task"].Value;
            string sfreturn = mc[0].Groups["return"].Value;
            string value = mc[0].Groups["value"].Value;
           MessageBox.Show(option+task+sfreturn+value);