Ok, after doing some more research, it looks like this may not be a trojan after all. What we're experiencing seems very similar to what is described here (WARNING, article contains links to sites which may infext your computer, don't click on them): http://www.dynamoo.com/diary/malware-scan-newbieadguide-com-hijack.htm

Basically, a banner ad that is getting served up through Google AdSense takes over the browser and redirects you to this malware site. I'm trying to get in touch to Google to makesure they stop serving this ad, but in the meantime, please be patient and DON'T INSTALL any software from untrusted soures. Thanks,

Bruno 

Looks like we may be dealing with some variant of the trojan described here. If you're experiencing these pop-ups, please send me an e-mail at bruno AT curbly.com. Please make sure to note which operating system and browser you're using, as well as the page on which you saw the ads (if you know it).