Could be an infected source code for a miner or wallet which is compiled on each platform (windows, linux etc) ...
My rigs don't have wallets running on them.
Infected source code in all sgminer, cgmniner, bfgminer, and even Cudaminer? Code I've downloaded from github and compiled myself in each case?
Seems highly unlikely. Possible, but very unlikely.
You seem to have a good sampling of configurations, so it seems like agood place to start. Do you they all run on the same local area network? If so, are they using private ip addresses with your router running network address transalation? Are they dynamically assigned or manually entered into the configuration of each mining computer?