Turning off Composr's custom 404 page in the htaccess helps lower performance impact (or saving it to a static HTML file and using that as the 404 page).
Instead of example.com one should probably use a non-existent site like gjkfjlgjlkdlkjgfljdkgjlfkd.com. Not nice for people in general to blackhole traffic to the same place, even if that place is designed to be super-efficient.
In the past I have just done mass IP blocks in .htaccess, or redirected the URLs they're trying off to example.com.
RewriteEngine on
# Misrouted traffic fix (12th Jan 2014)
RewriteRule ^baltimoreroot.* http://example.com/ [NC,R=301,L]
RewriteRule ^connect.* http://example.com/ [NC,R=301,L]
RewriteRule ^announce.* http://example.com/ [NC,R=301,L]
Turning off Composr's custom 404 page in the htaccess helps lower performance impact (or saving it to a static HTML file and using that as the 404 page).