A relative of mine gets a little too crazy with her PC. Despite repeated warnings, she'll still open email attachments with alacrity. So I just spent the last 20 minutes on the phone figuring out how to deal with the consequences.
It was a Trojan. She doesn't have a firewall, but a recently updated virus scanner caught the thing in an email from a friend of hers. I don't use Norton AntiVirus myself, so I don't know the details, but apparently the software "quarantined" the trojan. (Backdoor.Autoupder). This trojan supposedly is not widely spread, but it's loose in central Illinois for sure.
You might wonder what the firewall would have done. This trojan apparently contacts external machines to load more objects, which can be used for much mischief. Unlike many others, products like ZoneAlarm test outgoing traffic along with incoming, so if a mysterious program looks for access to the Web, you can deny it. In that way, even if a trojan gets installed, it can't call back to the mother ship and announce its presence. Then your PC can't be used for such things as distributed denial of service attacks like this.
If you have a broadband and don't have a firewall, kindly post your street address and a picture. That way we can all find you and knock you silly until you get with the program. ZoneAlarm is a freebie. Get it. Now!
UPDATE: I'm getting a disturbing number of Google hits on this one. It's fairly new, so make sure your antivirus program is up to date. Or else Quana and I will come and get you...