Who's making bogus web requests?

Yesterday I noticed in my Apache access log a lot of 404s that looked like this:

aaa.xx.65.186 - - [25/Jul/2007:05:55:05 -0500] "GET http://www.some-advertising-site.com/banner/digits HTTP/1.1" 404 305 "http://some-different-website.com/" "legitimate-looking agent"

Not only am I not hosting banner ads, the GET request is invalid. It should be GET /banner/digits..., without the scheme and hostname part of it. I wondered how many I had of these, and how many hits I was getting. A Perl one-liner to the rescue!

perl -MData::Dumper -nae'++$n{$F[0]} if /GET http/; \
    END{print Dumper\%n}' access.log

$VAR1 = {
          'aaa.xx.65.186' => 132, # Real IPs obscured
          'bb.yyy.7.60' => 48,
          'ccc.zzz.46.147' => 111,
          'dd.qq.71.82' => 33
        };

So it looked like I was getting hit by a couple of 0wnz0red boxes with some sort of virus on them. I added them to my iptables DROP list and was done with it.