PCs without virus protection are the most likely to become zombies, but even a protected PC can be infected if its antivirus software’s virus definitions are out of date or don’t properly detect certain compressed files.
If you are inclined to be even more proactive and you have the technical savvy, here are further recommendations
[http://isc.sans.org/diary.php?date=2004-10-11]from handler Deb Hale at the ISC:
“…Has your hosts file been rewritten? C:\windows\system32\drivers\etc
“…Do you have a lot of unidentified connects to the system? – Start – Run – cmd, at the command prompt type netstat -an. Take a look at the devices that are listed. Do you recognize all of the ips?
“…If you go into windows task manager (right-click taskbar, choose ‘task manager’) do you see any processes running that you don’t recognize?
“…If you are comfortable with regedit, go to HKEY_LOCAL_MACHINE – software – microsoft – windows – current version. You should see run and run once and run services, (you may or may not see run services). Do you see any entries that you don’t recognize or look suspicious?”