Seedy - 7:22 pm on May 20, 2012 (gmt 0)

I'm with you there, and Mozilla/4.0 coupled with all MSIE versions prior to 6.0 too (with an exception for SE's)

Perhaps something like:
RewriteCond %{HTTP_USER_AGENT} Mozilla/4 [NC] #AND
RewriteCond %{HTTP_USER_AGENT} MSIE/\ (1-6) [NC] #BUT NOT
RewriteCond %{HTTP_USER_AGENT} !(google|msn|bing) [NC]
RewriteRule 403.php [F]

?