Multithreading collision

private static string GenerateFileName2(CloudBlobDirectory container, string uploadFilePrefix)
{
    DateTime now = DateTime.Now;
    string nowString = now.ToString(CultureInfo.CurrentCulture.DateTimeFormat.SortableDateTimePattern);
    string result = uploadFilePrefix + nowString + "_000";

    var blob = container.GetBlockBlobReference(result);
    int i = 1;
    while (blob.Exists())
    {
        result = uploadFilePrefix + nowString + "_" + (i++).ToString("000");
        blob = container.GetBlockBlobReference(result);
    }

    return result;
}