Block that IP address in your firewall and see if this keeps up.
Not gonna work if he has a dynamic IP address which is what 99.9% of home users have.

Also, Downloader.Trojan is exactly that. A trojan that downloads other spyware/adware/virii nasty type stuff. I would say that this is a 'calling home' situation for sure. Let's see those FW logs though, (obscuring your own info of course)