how can I block the attack like this?

[fhal]

 Hi all,

Today my server was attacked. After checked Nginx access log, I found logs like below:



116.114.17.182 - - [04/Sep/2012:20:27:41 +0800] "GET /member.php??username=xxxx&rndnum=-1777927191 HTTP/1.1" 500 186 "-" "-" "-"

116.114.17.182 - - [04/Sep/2012:20:27:41 +0800] "GET /member.php??username=xxxx&rndnum=-1777927191 HTTP/1.1" 500 186 "-" "-" "-"

116.114.17.182 - - [04/Sep/2012:20:27:41 +0800] "GET /member.php??username=xxxx&rndnum=-1777927191 HTTP/1.1" 500 186 "-" "-" "-"




It seems the attacker was using some tool to attack my server. You can see that the user agent / browser version are blank.

Due to I can't block the blank user agent (some web browser is using blank user agent, for example, UC), is there any way can I use to block this kind of attack?




Thank
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