Do the Internet and yourself a favor, disconnect your LAN NOW. This keeps the virus from phoning home (so to speak) for more trojans to download, more targets to go after, etc.
Shut down all infected or suspect computers, as in, power them off.
Start with, or make a known good machine, either by re-installing it or unpacking it. Harden it. Make another if you have someone working with you, so you each have one to work from. Attached them to the Internet or the LAN, but never both (for now). Now you have a computer to work from.
Start with all your managed network equipment, routers, switches, firewalls and gateways. Make sure there are no hacks installed. Harden them. Now you have a LAN you can work on.
Disinfect suspect computers by pulling the hard drives and attaching them via USB adapter to the known good machine(s). If too far gone, reinstall.
Once you get to volume disinfecting/reinstallation, call in help. Temps, shipping/receiving clerks, admin assistances, interns, power users, if you tell management it will cut time they'll find someone to help you. Just having someone grab computers and put them all in a row will save you time to focus on the hard stuff.