Unknown device in disk utility

I went into disk utility today on my iMac.
I found an unknown hitachi device listed there.
Does this mean another device has hacked my computer?
Any advice would be appreciated. I use a shared network in a houseshare, but have my firewall and security set to maximum. I don't understand why this other pc is in the list and am worried about online banking, fraud etc.
Regards

Have a look in Finder and see if it is listed under Devices. If so Eject it.

Hi
Nothing in the finder.
Just listed in the disk utility.
Not sure whether his means another pc has hacked in while I'm not around?
Regards

I doubt very much you have been hacked.
Was your original HD Hitachi ?
If so I think your machine will have kept that name in Disk utility.

I have never owned a Hitachi hd.
I have a Seagate hd but that is listed as normal.

Highlight it in Disk Utility and click on Verify, what happenns

Also Click on Partition, what is there?

It checks everything then says partition map seems to be ok.
It just says macintosh HD.
Do mac use Hitachi Hard drives?

In Partition does it show any size?

Does it look like this?
Yes Apple uses Hitachi drives.

Yes it does.
I think that solves the problem.

The line that says Hitachi is the actual drive. The two offset ones below are the partitions - in this case 'snow' would show up in Finder as the drive, and 'Bootcamp' is the windows partition.
The 1 TB WD is my backup drive with 'Book' showing up in Finder.