c# - Web Client Exception: The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel

Question

I have a simple app that uses the C# Web Client class to download a websites HTML. This is a stripped down sample of the code I'm using:

WebClient wc = new WebClient();
wc.Headers.Add("user-agent",
    "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR 1.0.3705;)");
htmlCode = wc.DownloadString("https://www.oig.hhs.gov/exclusions/exclusions_list.asp");

There seems to be an issue with the websites certificate, because I encounter this exception:

The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel." "The remote certificate is invalid according to the validation procedure.

If you copy and paste the link into a browser, it requires you to agree to the risks before allowing you to view the site. Its a government website, so I'm not worried about any viruses or anything. Is there anyway to tell the web client to bypass this issue, and continue to the site?

Answer 1

As far as I know this is because they use a invalid or expired SSL certificate. You can bypass (ignore) it by using:

ServicePointManager.ServerCertificateValidationCallback += (sender, certificate, chain, sslPolicyErrors) => true;

Edit 2015:

This post is getting a lot of upvotes, but I regret my answer. It may remove your error, but it won't fix the issue. Accepting any SSL certificates will leave you vulnerable for man in the middle attacks, so it's generally a very bad idea. I will leave this answer for future reference, but please take note that you should try to fix the issue at the root, namely by making sure the SSL certificate is valid.