
It is possible, although somewhat difficult in practice, to trace the abuser of an open proxy or trojan.
Tracing distributed spam attacks - www.nsc.liu.se/~nixon/distspam/
Realtime Proxy Abuse Triangulation - www.unixwiz.net/rpat/
Reverse Proxy Tracing - www.brightok.net/~jbates/rproxy.txt
Tracking a Zombie Army - jameslick.com/zombies/Tracking%20A%20Zombie%20Army.pdf