Kudos to MemeStreams user Dagmar for putting together a post with breaks the technical aspects of Lynn's disclosure down in a way that non-technical people can understand. Be sure to click through and read his entire post.
Someone who takes the time to tie a few existing exploits together and utilize a technique similar to what Lynn discovered to make a worm that infects equipment, spends a small amount of time trying to infect other equipment, and then viciously puts the equipment out of commission in the aforementioned fashion, could in a very real sense turn off large chunks of the Internet.
No, I was not joking about the last sentence. If you work in an IT (Information Technology shop) take a moment to look around your office at all the very important equipment you have that just happens to have the Cisco logo on it. (I say "just happens to have the Cisco logo" because the root problem here has nothing to do with Cisco in particular, they're just the first company who have had this weakness uncovered--and as I said earlier, they were already in better shape than most.) Now imagine what would happen if that all that equipment just shut off, and you couldn't get it back up and running any time in the next twelve hours or so. You might think, "well, I will just go to their website and get the updates" but no, no... the Internet connection ran through one of the pieces of equipment that is now down so you can't do that. ...and even if it's not, there's a good chance that the people who your company connects to in order to reach the Internet has equipment that's has been effected, so you still can't get to the website with the updates you need. So you pick up the phone and call the manufacturer, and get to wait on hold for a very long time indeed, because many thousands of other people are just as stuck as you are. FedEx can get things out fast, but they're not nearly instantaneous, and hundreds of thousands of packages all marked "Red Tag, Highest Priority" at once are going to give them fits. Unless you know someone with magic powers of teleportation, you're looking at a very long wait for a package to be delivered by a truck that can fix your problem, and you're going to have to deal with all the upper-management types freaking out in the meantime. (Mind you, if you're lucky, your inter-office email system will also have been shut down by this, so they can only get to you through your cell phone and pager, which limits the number of panicked managers who can get to you at once.)
One message that Dagmar tries to get across in this, that should be spread and embraced, is that equipment (and software) mono-cultures are inherently dangerous. A post on the blog Art Of Noh offers the following good advice:
Which brings me down to the last and final lesson in the post, to nobody in particular: diversity.
Choose your hardware wisely, and don't rely on a single brand. If you have the budget to buy the no 1 hardware out there, buy one which is just as good and a little bit less expensive. Or if you have just about the budget to buy no 3, add a few more bucks and buy no 2. If your entire company network is based on routers from company X, buy a few from company Y as well. Of course, be sure to test their interoperability in the first place. Finally, when the unspeakable happens, don't panic. Just upgrade that flash and carry on.
Also, don't miss the most excellent video going around of Cisco's temp-workers ripping Mike's presentation out of the conference booklets. It can be found numerous places on the web, such as the Make Magazine blog.
Non-Technical Explanation of Mike Lynn's Disclosure