"Derek" on my router

[#1]

Hi,
I have password protection etc., but seem to have an expired "unknown" on my router called Derek. There is a Mac address and the IP is inline with my ip numbers, but we don't have a Derek in the house!
Is there anyway of tracing Derek?

[#2]

I take it, you have a wireless network?
And that you either don't have security setup, or the security you have is WEP.
Switch to WPA security and the unknown will vanish.
It's one of your neighbours using your internet rather than their own.

[#3]

As above, "Derek" was probably picking up his IP address off your DHCP server, which is why it's the same IP address range.

[#4]

I have the wireless setup up as WPA.
Yes, it has to be a neighbour, I will change the passwords again.
Thank you for confirming what I suspected
Thanks for taking the time.
N

[#5]

What's the MAC address? Finding out the device manufacturer might give some hints as to what/who/where the culprit is.
Mathew

[#6]

If someone is hacking your WPA security, they are determined and knowledgeable.
Whilst WPAis hackable, it makes an interloper less likely, are you sure theirs no mobile phones or other devices you may not initially think about that are connected?
However, having said that, the name "Derek" does suggest it's a Windows PC to me.

[#7]

Does your router, or wireless access point, have the facility to restrict access to (only your) MAC addresses ?
While some might say that a determined hacker could potentially spoof one of your PC's MAC addresses, it would give you another level of security.
In compiling your list of authorized MAC addresses, you may just discover "Derek" the IP enabled TV (or whatever) that you had forgotten about that suddenly stops working !