how to determine intruder

From: Dave (ddss@hotmail.com)
Date: 12/30/02 

From: "Dave" <ddss@hotmail.com>
Date: Mon, 30 Dec 2002 12:11:43 -0800

Bill,

If you downloaded Black Ice free from Kaaza.com or a
similiar peer-to-peer software program, someone may have
planted a Trojan in there also.

Dave
>-----Original Message-----
>We've had a hacker repeatedly probe our network from a
client machine. The
>puzzling thing is, it is always the same client machine.
We have changed
>the hard drive, network card, email address and computer
name, yet someone
>continues to find this client machine and perform port
scans on other
>machines on the network from this machine. We suspect
the intruder may be
>getting in via the internet, but are not sure. We have
Black Ice running on
>this machine, but it intermittently turns off for unknown
reasons. Can
>anyone recommend tools or ideas to help figure out what
the intruder
>software is and how it may be reaching client machine?
>
>Thanks
>Bill
>
>
>.
>