An intrusion attempt by c71585.com was blocked

About a week ago I started receiving the following alert from Norton:

An intrusion attempt by c71585.com was blocked. System infected Trojan.zbot activity 15

I got the following information from Norton:

Attacking computer 31.184.194.6,80

Attacker url c71585.com/z

Network traffic from c71585.com/z matches the signature of a known attack.  The attack was resulted from \device\harddiskvolume2\windows\syswow64\dllhost.exe to stop being notified for this type of traffic, in the actions panel click stop notifying me

I get this alert about twice a day and Norton says the attacked was stopped and no further action is required.

I ran a full scan of Norton and malwaresbyte and Norton Trojan removal and they all found nothing.  I tried to run power eraser and get a can't find specified file error every time. 

What is this?

Thanks,