We may not know what the Conficker authors have in store for us on April 1st, but I doubt many network administrators want to find out. Maybe they don’t have to: I’ve been working with the Honeynet Project’s Tillmann Werner and Felix Leder, who have been digging into Conficker’s profile on the network. What we’ve found is pretty cool: Conficker actually changes what Windows looks like on the network, and this change can be detected remotely, anonymously, and very, very quickly. You can literally ask a server if it’s infected with Conficker, and it will tell you. Tillmann and Felix have their own proof of concept scanner, and with the help of Securosis‘ Rich Mogull and the multivendor Conficker Working Group, enterprise-class scanners should already be out from Tenable (Nessus), McAfee/Foundstone, nmap, ncircle, and Qualys.

We figured this out on Friday, and got code put together for Monday. It’s been one heck of a weekend.

The technical details are not complicated — Conficker, in all its variants, makes NetpwPathCanonicalize() work quite a bit differently than either the unpatched or the patched MS08-067 version — but I’ll let Tillmann and Felix describe this in full in their “Know Your Enemy” paper, due out any day now with all sorts of interesting observations about this annoying piece of code. (We didn’t think it made sense to hold up the scanner while finishing up a few final edits on the paper.)