VirusTotal virusTotal = new VirusTotal("YOUR API KEY HERE");

//Use HTTPS instead of HTTP
virusTotal.UseTLS = true;

//Create the EICAR test virus. See http://www.eicar.org/86-0-Intended-use.html
byte[] eicar = Encoding.ASCII.GetBytes(@"X5O!P%@AP[4\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*");

//Check if the file has been scanned before.
FileReport report = await virusTotal.GetFileReportAsync(eicar);

Console.WriteLine("Seen before: " + (report.ResponseCode == FileReportResponseCode.Present ? "Yes" : "No"));