(Update: On second thought, never mind. AVG has seen the error of their ways and the other code simply keeps logs from showing the Live Search referrer data. I'm blocking the log data a different way now.)
I've spent the last umpteen hours scouring the Internet for this information. There are two robot sources using JavaScript robots and causing extra AdSense impressions. They had to be terminated.
Here are the .htaccess rules that can stop them both:
# block spurious referrals from microsoft LVSP, LIVSOP or QBHP
RewriteCond %{REMOTE_ADDR} ^65\.55\.(109|110|165|232) [OR]
RewriteCond %{REMOTE_ADDR} ^131\.107\.0\.9[56]
RewriteCond %{HTTP_REFERER} FORM=(LVSP|LIVSOP|QBHP)$ [NC]
RewriteRule .* - [F]# here we assume certain MSIE 6.0 agents are from linkscanner
# redirect these requests back to avg in the hope they'll see their silliness
RewriteCond %{HTTP_USER_AGENT} ".*MSIE 6.0; Windows NT 5.1; SV1.$" [OR]
RewriteCond %{HTTP_USER_AGENT} ".*MSIE 6.0; Windows NT 5.1;1813.$"
RewriteCond %{HTTP_REFERER} ^$
RewriteCond %{HTTP:Accept-Encoding} ^$
RewriteRule ^.* http://www.avg.com/?LinkScannerSucks [R=307,L]
Sources: Using AVG linkscanner against itself and Stupid search.live.com and form=QBHP
