Pfui - 3:32 pm on Nov 18, 2011 (gmt 0)

Whatever this is --

Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/534+ (KHTML, like Gecko)

-- that's running amok on IncrediBill's and HenryUK's sites from MSN, also has an atypical + in the "Kit/" version spot in addition to missing the post-"Gecko)" version number. So the preceding example --

RewriteCond %{HTTP_USER_AGENT} Gecko\)$ [NC]
(Note: I escaped the closing paren)

-- or a variation on a theme --

RewriteCond %{HTTP_USER_AGENT} ^Mozilla.*Gecko\)$ [NC]

-- should suffice, imo, regardless of REMOTE_ADDR. I don't care where it comes from, it's not getting in.