Network Security Map - New Device Connects with different IP Addresses

Just recently upgraded to Norton 360 ver 5 from version 4.  I should mention that I have a wired connection to a motorolla modem (no router). I noticed that I had a new device connected in my network security map.  I watched this device connect, disconnect and come back online all by itself with different IP addresses each time 3 times in 5 minutes.  The IP address of this device started with 26.... the first time, then started with 69 the second, until the third time it matched my pc IP address.  I refreshed after this to try and get more information about the device and the device name was 'Cisco' something.  I refreshed again and the device moved into the trust control tab by itself. 

 

I've read others' posts about this and most have mentioned that it was possibly their modem, but I don't have a Cisco modem and there was no mention of connecting to my pc with different IP addresses and then moving to the trust control tab either. 

 

Since that, I purged my network and the device is now gone.  Can someone tell me whether I have another computer/trojan etc... attacking my pc?

 

Thanks!