What information should I log if I detect that my site is under attack?

In the code below if I get into the if statement I can safely say my site is under attack. What information is it a good idea to log?

Any recommendations on actions that开发者_StackOverflow can be taken to minimize the damage at this point?

protected void btn_Search_Click(object sender, EventArgs e)
{
   if(tb_SearchBox.Text.Length > tb_SearchBox.MaxLength)
   {
      //What should i log?
      //What actions should I take?
   }
   //Otherwise search
}

For the action I would just redirect them to error page.

For the logging I would do as @The Rook mentioned and grab the entire request. I would use some logging software, such as ELMAH. ELMAH captures the entire HTTP Request as well as referrer IP. Logging is good regardless of security concerns

You can log the ip and log how many times he has already attempted to hack you. If it's above a certain threshhold you can block his ip for a certain amount of time

When a Web application firewall like Mod_Security detects an attack it will log the entire HTTP request, along with the remote IP address.