Extention method for web service url address

WebServiceExtention.cs

public static class WebServiceExtention
{
    public static bool isValidWebServiceUrl(this string url)
    {
        bool rv = true;
        if (String.IsNullOrEmpty(url))
            rv = false;

        string Http_URL = HttpUtility.UrlDecode(url);

        HttpWebRequest ObjReq = (HttpWebRequest)HttpWebRequest.Create(Http_URL);
        ObjReq.Timeout = 36000;
        ObjReq.UseDefaultCredentials = true;

        try
        {
            if (ObjReq.GetResponse().ContentLength < 0)
                rv = false;
        }
        catch (Exception)
        {
            rv = false;
        }
        return rv;
    }
}