Stopping open proxies and open relays

[Adi Linden <adil () adis on ca>]

I am looking for ideas to stop the spam created by compromised Windows 
PC's. This is not about the various worms and viruses replicating but 
these boxes acting as open relays or open proxies.

There are valid reasons not to run antivirus software, coupled with 
clueless users, this results in machines that SPAM again just a few hours 
after having been cleaned.

Adi