I am trying to remove an interesting trojan from a Windows XP computer.

It manifests itself as a phishing page (screenshot linked) that appears after the user tries to log on to eBay. So far, I haven't found any other web sites that are affected. As you can see, the trojan intercepts browser connections (all installed browsers are affected) and injects this phishing page. The address looks like it's ebay.com, but HTTPS verification doesn't work (no lock icon or green bar in Firefox.)

At some point, Trojan.Dropper appeared on the computer. I removed it with Malwarebytes Anti-Malware. Although it reappeared several times, it seemed to be gone after I booted into Safe Mode and did a full system scan with MBAM.

Now, however, a different trojan has appeared on the machine; I suspect it was installed by Trojan.Dropper. So far, MBAM, Ad-Aware, and Spybot S&D have been unable to remove it. I've looked for it in the HijackThis log but haven't found anything conclusive.

Has anyone run across a trojan like this before? Where would I start looking for it to remove it manually?

Thank you for reading.