how to block a special UA

[guest*]

Hi,

can somebody please help me with a code for my .htaccess? I want to block a special User which is comming with a dynamic IP, but a special Agent. He is spaming my site and trying to attack code manually. It's a human I'm sure.

His bowser is:

Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; GTB6.6; . NET CLR 2.0.50727; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)

I've already added this:

RewriteCond %{HTTP_USER_AGENT} ^$ [OR,NC]
RewriteCond %{HTTP_USER_AGENT} and here the code for this special agent, which I don't know how to write
RewriteRule ^(.*)$ - [F,L]

Thxs. for the help in advance