<rewrite>
  <rules>
    <rule name="Ban user-agent RogueBot" stopProcessing="true">
      <match url=".*" />
      <conditions>
        <add input="{HTTP_USER_AGENT}" pattern="RogueBotName" />
        <add input="{MyPrivatePages:{REQUEST_URI}}" pattern="(.+)" />
      </conditions>
      <action type="AbortRequest" />
    </rule>
  </rules>
  <rewriteMaps>
    <rewriteMap name="MyPrivatePages">
      <add key="/PrivatePage1.aspx" value="block" />
      <add key="/PrivatePage2.aspx" value="block" />
      <add key="/PrivatePage3.aspx" value="block" />
    </rewriteMap>
  </rewriteMaps>
</rewrite>

public class UserAgentBasedRedirecter : IHttpModule
{
    private static readonly Regex _bannedUserAgentsRegex = null;
    private static readonly string _bannedAgentsRedirectUrl = null;

    static UserAgentBasedRedirecter()
    {
            _bannedAgentsRedirectUrl = ConfigurationManager.AppSettings["UserAgentBasedRedirecter.RedirectUrl"];
            if (String.IsNullOrEmpty(_bannedAgentsRedirectUrl))
                _bannedAgentsRedirectUrl = "~/Does/Not/Exist.html";

            string regex = ConfigurationManager.AppSettings["UserAgentBasedRedirecter.UserAgentsRegex"];
            if (!String.IsNullOrEmpty(regex))
                _bannedUserAgentsRegex = new Regex(regex, RegexOptions.IgnoreCase | RegexOptions.Compiled);
    }

    #region Implementation of IHttpModule

    public void Init(HttpApplication context)
    {
            context.PreRequestHandlerExecute += RedirectMatchedUserAgents;
    }

    private static void RedirectMatchedUserAgents(object sender, System.EventArgs e)
    {
            HttpApplication app = sender as HttpApplication;

            if (_bannedUserAgentsRegex != null &&
                app != null && app.Request != null && !String.IsNullOrEmpty(app.Request.UserAgent))
            {
                if (_bannedUserAgentsRegex.Match(app.Request.UserAgent).Success)
                {
                    app.Response.Redirect(_bannedAgentsRedirectUrl);
                }
            }
    }

    public void Dispose()
    { }

    #endregion
}

<configuration>
	<appSettings>
		<add key="UserAgentBasedRedirecter.UserAgentsRegex" value="^msnbot/1.1" />
	</appSettings>
...
	<system.web>
		<httpModules>
			<add name="UserAgentBasedRedirecter" type="Andies.Web.Traffic.UserAgentBasedRedirecter, Andies.Web" />
		</httpModules>
	</system.web>
</configuration>

SetEnvIf User-Agent ^$ spammer=yes     # block blank user agents

Order allow,deny
allow from all
deny from env=spammer