Just what we need. Netcraft reports a worm that installs a network sniffer.

What’s that? It’s a program that listens in on traffic going across your network, looking for things like, oh, login names and passwords, credit card numbers, etc. They’re the reason online commerce requires SSL encryption.

Sniffers work because of the way ethernet is designed. Basically your local network is like holding a conversation in a crowded room. You focus on the people you’re talking with, and you tune out other people as best as you can. (In this case there’s also someone at the door who can relay your words to someone in another room, and relay back their responses.) To hold a private conversation you have to go somewhere else or talk in code. A traffic sniffer just doesn’t tune anyone out, so it picks up on everything in your local network.

So now, no matter how well you guard your own computer, if some moron on your network manages to get infected by Worm.SDBot (which thankfully hasn’t been spotted “in the wild” yet), you could still be handing out your email login/password when you log onto Yahoo/Hotmail/Outlook/etc.

You just might want to use that “secure login” option. Assuming, of course, that you have one.